feat: per-extraction OCR language override

Allow users to specify a Tesseract language string (e.g. jpn+jpn_vert)
on a per-extraction basis, overriding the global OCR language setting.

- Add payload column to ai_jobs table (migration) to carry per-call data
- Thread ocrLanguages payload through enqueueJob → processNextJob → extractItemText
- New GET /api/ai-settings/ocr endpoint (requireAuth) returns { ocrMode, ocrLanguages }
- ImageLightbox fetches OCR settings and shows a language input next to the
  Extract Text button when mode is hybrid or tesseract (hidden for llm-only)
- MixedView fetches OCR settings and passes them down to EntryTile; kebab
  Extract Text on images shows an inline language prompt before dispatching the job

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/db.ts

@@ -338,4 +338,12 @@ function migrateAiJobs(db: Database.Database): void {
     CREATE INDEX IF NOT EXISTS ai_jobs_status ON ai_jobs(status);
     CREATE INDEX IF NOT EXISTS ai_jobs_created_at ON ai_jobs(created_at);
   `)
+
+  // Add payload column if not present
+  const aiJobsRow = db
+    .prepare("SELECT sql FROM sqlite_master WHERE type='table' AND name='ai_jobs'")
+    .get() as { sql: string } | undefined
+  if (aiJobsRow && !aiJobsRow.sql.includes('payload')) {
+    db.exec('ALTER TABLE ai_jobs ADD COLUMN payload TEXT')
+  }
 }