feat: implement bidirectional annotation sync and delete propagation

Bring the plugin to feature parity with the server's annotation sync
system. Previously annotations were push-only (and even that was broken
because the server ignored inline annotations in progress pushes).

ANNOTATION PULL (server → device):
  - Add applyServerAnnotations() method called from _doGetProgress
    after progress handling
  - Parses annotations.highlights, annotations.notes, and
    annotations.bookmarks from GetMetadata response
  - Matches incoming annotations against local bookmarks by pos0
    (start position) to detect existing entries
  - New entries are inserted with correct KOReader bookmark format:
    page, pos0, pos1, datetime, text, notes, color, chapter
  - Existing entries with changed content are updated (LWW: server
    version is authoritative since the server already resolved conflicts)
  - Respects sync_highlights, sync_notes, sync_bookmarks toggles for
    inbound sync, not just outbound
  - Triggers onSortBookmarks + saveSettings on change for persistence

DELETE PROPAGATION:
  - Parses annotations.deleted_highlights and annotations.deleted_bookmarks
    from GetMetadata response
  - Each entry contains device_sync_data (pos0, datetime, page) from the
    original device push
  - Matches local bookmarks by pos0 and removes them
  - Deleted highlights only remove entries that have text (to avoid
    removing plain bookmarks at the same position)

CLEANUP:
  - Fix BookhoardAPI.lua: rename pcall return _ to err for clarity
    (was functional but misleading variable name)
  - Remove dead code: unused getLibrary() and syncBookmarks() API methods
  - Remove sync_endpoints field (stored from registration response but
    never read by any code)

BookhoardAPI.lua

@@ -60,23 +60,23 @@ function BookhoardAPI:_request(method, path, body, timeouts)
 
     socketutil:set_timeout(timeouts[1], timeouts[2])
 
-    local ok, _, code
+    local ok, err, code
     if url:match("^https://") then
         if ssl_ok then
-            ok, _, code = pcall(ssl_https.request, request)
+            ok, err, code = pcall(ssl_https.request, request)
         else
             socketutil:reset_timeout()
             return false, { error = "HTTPS not supported on this device" }
         end
     else
-        ok, _, code = pcall(http.request, request)
+        ok, err, code = pcall(http.request, request)
     end
 
     socketutil:reset_timeout()
 
     if not ok then
-        logger.warn("BookhoardAPI: request failed:", _)
+        logger.warn("BookhoardAPI: request failed:", err)
-        return false, { error = tostring(_) }
+        return false, { error = tostring(err) }
     end
 
     local response_body = table.concat(sink)
@@ -130,12 +130,6 @@ function BookhoardAPI:getMetadata(uuid)
     return self:_request("GET", "/api/sync/koreader/metadata/" .. uuid, nil, PROGRESS_TIMEOUTS)
 end
 
-function BookhoardAPI:getLibrary()
-    return self:_request("GET", "/api/sync/koreader/library", nil, PROGRESS_TIMEOUTS)
-end
 
-function BookhoardAPI:syncBookmarks(data)
-    return self:_request("POST", "/api/sync/koreader/bookmarks", data, PROGRESS_TIMEOUTS)
-end
 
 return BookhoardAPI

main.lua

@@ -68,7 +68,6 @@ Bookhoard.default_settings = {
     sync_highlights = true,
     sync_notes = true,
     sync_mode = SYNC_MODE.IMMEDIATE,
-    sync_endpoints = nil,
 }
 
 function Bookhoard:init()
@@ -212,7 +211,6 @@ function Bookhoard:buildMainMenu()
                     ok_callback = function()
                         self.settings.auth_token = nil
                         self.settings.device_id = nil
-                        self.settings.sync_endpoints = nil
                         self.settings.auto_sync = false
                         G_reader_settings:saveSetting(self.settings_key, self.settings)
                         self:registerEvents()
@@ -623,7 +621,6 @@ function Bookhoard:startRegistrationPoll()
             self.registration_id = nil
             self.settings.auth_token = result.auth_token
             self.settings.device_id = result.device_id and tostring(result.device_id) or nil
-            self.settings.sync_endpoints = result.sync_endpoints
             G_reader_settings:saveSetting(self.settings_key, self.settings)
             self:registerEvents()
             self:setupOPDS()
@@ -1039,6 +1036,10 @@ function Bookhoard:_doGetProgress(interactive)
             return
         end
 
+        if result.annotations then
+            self:applyServerAnnotations(result.annotations)
+        end
+
         local progress = result.progress
         local percentage = self:getLastPercent()
         local server_percentage = progress.percentage or 0
@@ -1100,6 +1101,118 @@ function Bookhoard:_doGetProgress(interactive)
     end)
 end
 
+function Bookhoard:applyServerAnnotations(annotations)
+    if not self.ui.bookmark or not self.ui.bookmark.bookmarks then
+        return
+    end
+    if not annotations then return end
+
+    local local_bms = self.ui.bookmark.bookmarks
+    local changed = false
+    local has_pages = self.ui.document.info.has_pages
+
+    local function findLocalByPos0(pos0)
+        for i, bm in ipairs(local_bms) do
+            if bm.pos0 == pos0 then
+                return i
+            end
+        end
+        return nil
+    end
+
+    local function makePageFromPos(pos0)
+        if has_pages then
+            local page = tonumber(pos0:match("(%d+)$"))
+            return page or pos0
+        end
+        return pos0
+    end
+
+    local function addOrUpdate(server_entry, has_text)
+        local pos0 = server_entry.pos0 or ""
+        if pos0 == "" then return end
+        local idx = findLocalByPos0(pos0)
+        if idx then
+            local bm = local_bms[idx]
+            local srv_text = server_entry.text or ""
+            local srv_notes = server_entry.notes or ""
+            if (bm.text or "") ~= srv_text or (bm.notes or "") ~= srv_notes then
+                bm.text = srv_text
+                bm.notes = srv_notes
+                if server_entry.color then bm.color = server_entry.color end
+                changed = true
+            end
+        else
+            local entry = {
+                page = makePageFromPos(pos0),
+                pos0 = pos0,
+                pos1 = server_entry.pos1 or pos0,
+                datetime = server_entry.datetime or "",
+                text = server_entry.text or "",
+                notes = server_entry.notes or "",
+            }
+            if server_entry.color then entry.color = server_entry.color end
+            if server_entry.chapter then entry.chapter = server_entry.chapter end
+            table.insert(local_bms, entry)
+            changed = true
+        end
+    end
+
+    if self.settings.sync_highlights and annotations.highlights then
+        for _, hl in ipairs(annotations.highlights) do
+            addOrUpdate(hl, true)
+        end
+    end
+
+    if self.settings.sync_notes and annotations.notes then
+        for _, note in ipairs(annotations.notes) do
+            addOrUpdate(note, true)
+        end
+    end
+
+    if self.settings.sync_bookmarks and annotations.bookmarks then
+        for _, bm in ipairs(annotations.bookmarks) do
+            addOrUpdate(bm, false)
+        end
+    end
+
+    if annotations.deleted_highlights then
+        for _, del in ipairs(annotations.deleted_highlights) do
+            local pos0 = del.pos0 or ""
+            if pos0 ~= "" then
+                local idx = findLocalByPos0(pos0)
+                if idx and (local_bms[idx].text or "") ~= "" then
+                    table.remove(local_bms, idx)
+                    changed = true
+                end
+            end
+        end
+    end
+
+    if annotations.deleted_bookmarks then
+        for _, del in ipairs(annotations.deleted_bookmarks) do
+            local pos0 = del.pos0 or ""
+            if pos0 ~= "" then
+                local idx = findLocalByPos0(pos0)
+                if idx then
+                    table.remove(local_bms, idx)
+                    changed = true
+                end
+            end
+        end
+    end
+
+    if changed then
+        if self.ui.bookmark.onSortBookmarks then
+            self.ui.bookmark:onSortBookmarks()
+        end
+        if self.ui.saveSettings then
+            self.ui:saveSettings()
+        end
+        logger.dbg("Bookhoard: annotations updated from server")
+    end
+end
+
 function Bookhoard:_showSyncedMessage()
     UIManager:show(InfoMessage:new{
         text = _("Progress has been synchronized."),