feat(db): add context_text column to reading_progress

Stores surrounding text (~100 chars) at the reader's current position.
Used as fallback for CFI resolution when converting between epubcfi
and CREngine XPointer formats.

Updates:
- schema.sql: add context_text TEXT column, update stored procedure
- queries.sql: add context_text to GetUniversalProgress and
  UpdateUniversalProgress queries
- Regenerate sqlc Go code (models.go, querier.go, queries.sql.go)

internal/database/queries/queries.sql

@@ -793,6 +793,7 @@ SELECT
     rp.percentage,
     rp.character_offset,
     rp.epubcfi,
+    rp.context_text,
     rp.chapter,
     rp.chapter_progress,
     rp.viewport_x,
@@ -825,6 +826,7 @@ INSERT INTO reading_progress (
     percentage,
     character_offset,
     epubcfi,
+    context_text,
     chapter,
     chapter_progress,
     viewport_x,
@@ -842,13 +844,14 @@ INSERT INTO reading_progress (
     last_read_at
 )
 VALUES (
-    $1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14, $15, $16, NOW(), $17, $18, NOW()
+    $1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14, $15, $16, $17, NOW(), $18, $19, NOW()
 )
 ON CONFLICT (media_item_id, user_id)
 DO UPDATE SET
     percentage = EXCLUDED.percentage,
     character_offset = EXCLUDED.character_offset,
     epubcfi = EXCLUDED.epubcfi,
+    context_text = EXCLUDED.context_text,
     chapter = EXCLUDED.chapter,
     chapter_progress = EXCLUDED.chapter_progress,
     viewport_x = EXCLUDED.viewport_x,
@@ -1162,6 +1165,15 @@ JOIN media_items mi ON sc.media_item_id = mi.id
 WHERE sc.user_id = $1
 ORDER BY sc.created_at DESC;
 
+-- name: HasRecentConflictResolution :one
+SELECT EXISTS(
+    SELECT 1 FROM sync_conflicts
+    WHERE media_item_id = $1
+    AND user_id = $2
+    AND resolution_status != 'unresolved'
+    AND resolved_at > NOW() - INTERVAL '10 minutes'
+);
+
 -- ============================================
 -- KOREADER SYNC PROTOCOL
 -- ============================================