feat(analysis): add ocrs OCR backend and OCR-driven page text search

Adds an in-process ocrs OCR backend as the active analysis engine
(vision left dormant), enables OCR text search on the page-tag
aggregation endpoints, and reshapes the admin analysis/settings UI to
present the OCR-only surface. Bumps version 0.89.0 -> 0.90.0.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/.gitignore

@@ -1,3 +1,7 @@
 /target
 /.sqlx
 .env
+
+# Local OCR models for native dev (downloaded, not source)
+models/
+*.rten