feat(labs): add local-OCR text mode for image-blind AI providers

Add an opt-in in-browser OCR path so a user whose provider cannot read
images (ChatGPT-OAuth/Codex, a text-only model) can still scan a lab
report. The capability probe gains a `mode` field: `vision` when the
provider reads the image directly, `text` when local OCR is enabled and
any provider is configured, or null. The extract route grows a text
branch that accepts the in-browser-OCR'd text as JSON and structures it
through the existing schema + review/commit flow; the raw image never
reaches the server in text mode. New `labsLocalOcrEnabled` user column
(migration 0184, default off) gates it, with a dedicated PATCH endpoint.

package.json

@@ -87,6 +87,7 @@
     "sax": "^1.6.0",
     "sonner": "^2.0.7",
     "tailwind-merge": "^3.6.0",
+    "tesseract.js": "^7.0.0",
     "undici": "^8.5.0",
     "web-push": "^3.6.7",
     "yaml": "^2.8.4",