Sync fixes for underpowered devices: thin client, server-heavy

- collectAnnotations no longer calls getPageFromXPointer per
  annotation (a CRE-engine lookup each — the most expensive thing the
  sync loop did on weak hardware). Paging documents compute
  percentage arithmetically; CRE documents omit it entirely and the
  server derives it from the locator against the actual book.
- chapter/page are sent raw; the server's tolerant types accept
  strings, empty strings, and CRE xpointers in the page field.
  Previously a single annotation with chapter:'' failed the ENTIRE
  progress push with a 400, silently killing progress sync too.
- applyServerAnnotations validates pos0 before applying: rolling
  documents require '/body/...' xpointers, paging documents numeric
  pages. Unplaceable locators are skipped instead of becoming junk
  local bookmarks that would re-push as duplicates.

main.lua

@@ -827,19 +827,21 @@ function Bookhoard:collectAnnotations()
     if not all_bookmarks then
         return bookmarks, highlights, notes
     end
-
     local file_sha256 = self:getFileSHA256()
     local total_pages = self.ui.document:getPageCount()
+    local has_pages = self.ui.document.info.has_pages
 
     for _, bm in ipairs(all_bookmarks) do
-        local page_num = bm.page
-        if type(page_num) == "string" and self.ui.document.info.has_pages == false then
-            page_num = self.ui.document:getPageFromXPointer(page_num)
-        end
-        page_num = tonumber(page_num) or 0
+        -- Thin-client policy: no per-annotation CRE lookups here (a
+        -- getPageFromXPointer call each is the most expensive thing this
+        -- loop can do on weak hardware). Percentages are arithmetic for
+        -- paging documents and simply omitted for CRE documents — the
+        -- server derives them from the locator against the actual book.
+        local page_num = tonumber(bm.page) or 0
+        local percentage = has_pages and total_pages > 0 and (page_num / total_pages) or nil
 
-        local percentage = total_pages > 0 and (page_num / total_pages) or 0
         local chapter = bm.chapter or ""
+        if type(chapter) == "table" then chapter = "" end
 
         local entry = {
             chapter = chapter,
@@ -849,9 +851,11 @@ function Bookhoard:collectAnnotations()
             pos1 = bm.pos1 or "",
             page = tostring(bm.page or ""),
             text = bm.text or "",
-            percentage = Math.roundPercent(percentage),
             book_sha256 = file_sha256,
         }
+        if percentage then
+            entry.percentage = Math.roundPercent(percentage)
+        end
 
         local has_text = bm.text and bm.text ~= ""
         local has_notes = bm.notes and bm.notes ~= ""
@@ -1159,9 +1163,23 @@ function Bookhoard:applyServerAnnotations(annotations)
         return pos0
     end
 
+    local function isValidPos0(pos0)
+        -- Rolling (CRE) documents address bookmarks/highlights by xpointer;
+        -- paging documents (PDF/comics/DjVu) by page number. Anything else
+        -- (a raw "cfi:" locator, an epubcfi(...) string, a JSON anchor, …)
+        -- cannot be placed in this document and must not become a local
+        -- bookmark: it could never be matched again and would be re-pushed
+        -- to the server as a junk duplicate on the next sync.
+        if pos0 == "" then return false end
+        if has_pages then
+            return tonumber(pos0) ~= nil
+        end
+        return pos0:sub(1, 7) == "/body/"
+    end
+
     local function addOrUpdate(server_entry, has_text)
         local pos0 = server_entry.pos0 or ""
-        if pos0 == "" then return end
+        if not isValidPos0(pos0) then return end
         local idx = findLocalByPos0(pos0)
         if idx then
             local bm = local_bms[idx]