feat(db): add annotation sync schema, queries, and tombstone support

Add migration columns to media_highlights, media_notes, and media_bookmarks
for cross-device annotation sync:

- dedup_key: SHA-1 of normalized selection text + bucketed position, used
  as the stable cross-device identity for annotations
- last_modified_at / last_modified_source: edit clock for LWW resolution
  and cross-source conflict detection
- deleted / deleted_at: sticky tombstone columns for delete-wins semantics
  with a 30-day TTL before rows are physically purged
- note_text on highlights: stores attached notes from KOReader entries that
  have both selected text and a user note
- Location columns on bookmarks (cfi_position, percentage_location,
  epubcfi_location, chapter_reference, paragraph_reference)
- device_sync_data JSONB on all three tables: stores per-device native
  identifiers (e.g. KOReader pos0/datetime, Kobo bookmark_id) so each
  device can locate and manipulate its own copy of an annotation

Add partial unique indexes on (user_id, media_item_id, dedup_key) where
deleted = FALSE to enforce one active annotation per dedup key.

Add tombstone purge indexes on (deleted, deleted_at) for efficient GC.

New queries:
- GetByDedupKey for all three tables (returns active or most-recent tombstone)
- CreateFull / UpdateForSync for all three tables (populate sync columns)
- TombstoneByDedupKey / TombstoneByID for all three tables
- PurgeExpired* for all three tables (GC past TTL)
- GetActiveAnnotationsForBook (filtered union of highlights + notes)
- GetTombstonedAnnotationsForBook (union of all 3 deleted within TTL)
- GetMediaBookmarks with deleted filter
- GetMediaBookmark (singular) with deleted filter
- Added deleted=FALSE filter to GetMediaHighlights, GetAnnotationsForBook
- CreateAutoResolvedSyncConflict (INSERT with resolution_status='auto_resolved')

database/schema/schema.sql

@@ -1312,3 +1312,48 @@ CREATE TABLE IF NOT EXISTS media_bookmarks (
 
 CREATE INDEX IF NOT EXISTS idx_media_bookmarks_media ON media_bookmarks(media_item_id);
 CREATE INDEX IF NOT EXISTS idx_media_bookmarks_user ON media_bookmarks(user_id);
+
+-- ============================================
+-- ANNOTATION SYNC MIGRATIONS
+-- Adds dedup_key, LWW timestamps, soft-delete,
+-- and device_sync_data to annotation tables.
+-- ============================================
+
+ALTER TABLE media_highlights ADD COLUMN IF NOT EXISTS dedup_key VARCHAR(40);
+ALTER TABLE media_highlights ADD COLUMN IF NOT EXISTS last_modified_at TIMESTAMPTZ;
+ALTER TABLE media_highlights ADD COLUMN IF NOT EXISTS last_modified_source VARCHAR(30);
+ALTER TABLE media_highlights ADD COLUMN IF NOT EXISTS note_text TEXT;
+ALTER TABLE media_highlights ADD COLUMN IF NOT EXISTS deleted BOOLEAN DEFAULT FALSE;
+ALTER TABLE media_highlights ADD COLUMN IF NOT EXISTS deleted_at TIMESTAMPTZ;
+
+ALTER TABLE media_notes ADD COLUMN IF NOT EXISTS dedup_key VARCHAR(40);
+ALTER TABLE media_notes ADD COLUMN IF NOT EXISTS last_modified_at TIMESTAMPTZ;
+ALTER TABLE media_notes ADD COLUMN IF NOT EXISTS last_modified_source VARCHAR(30);
+ALTER TABLE media_notes ADD COLUMN IF NOT EXISTS deleted BOOLEAN DEFAULT FALSE;
+ALTER TABLE media_notes ADD COLUMN IF NOT EXISTS deleted_at TIMESTAMPTZ;
+
+ALTER TABLE media_bookmarks ADD COLUMN IF NOT EXISTS dedup_key VARCHAR(40);
+ALTER TABLE media_bookmarks ADD COLUMN IF NOT EXISTS last_modified_at TIMESTAMPTZ;
+ALTER TABLE media_bookmarks ADD COLUMN IF NOT EXISTS last_modified_source VARCHAR(30);
+ALTER TABLE media_bookmarks ADD COLUMN IF NOT EXISTS device_sync_data JSONB;
+ALTER TABLE media_bookmarks ADD COLUMN IF NOT EXISTS percentage_location FLOAT;
+ALTER TABLE media_bookmarks ADD COLUMN IF NOT EXISTS epubcfi_location TEXT;
+ALTER TABLE media_bookmarks ADD COLUMN IF NOT EXISTS chapter_reference INTEGER;
+ALTER TABLE media_bookmarks ADD COLUMN IF NOT EXISTS deleted BOOLEAN DEFAULT FALSE;
+ALTER TABLE media_bookmarks ADD COLUMN IF NOT EXISTS deleted_at TIMESTAMPTZ;
+
+CREATE UNIQUE INDEX IF NOT EXISTS idx_media_highlights_dedup
+    ON media_highlights (user_id, media_item_id, dedup_key)
+    WHERE dedup_key IS NOT NULL AND deleted = FALSE;
+
+CREATE UNIQUE INDEX IF NOT EXISTS idx_media_notes_dedup
+    ON media_notes (user_id, media_item_id, dedup_key)
+    WHERE dedup_key IS NOT NULL AND deleted = FALSE;
+
+CREATE UNIQUE INDEX IF NOT EXISTS idx_media_bookmarks_dedup
+    ON media_bookmarks (user_id, media_item_id, dedup_key)
+    WHERE dedup_key IS NOT NULL AND deleted = FALSE;
+
+CREATE INDEX IF NOT EXISTS idx_media_highlights_deleted_at ON media_highlights(deleted_at) WHERE deleted = TRUE;
+CREATE INDEX IF NOT EXISTS idx_media_notes_deleted_at ON media_notes(deleted_at) WHERE deleted = TRUE;
+CREATE INDEX IF NOT EXISTS idx_media_bookmarks_deleted_at ON media_bookmarks(deleted_at) WHERE deleted = TRUE;