Move panel detection dependencies to optionalDependencies

Fix npm install errors and make ML/CV libraries truly optional.

Changes:
- Move dependencies from "dependencies" to "optionalDependencies"
- Fix @techstark/opencv-js version from "^4.12.0" to "4.12.0-release.1"
  - The caret syntax (^) doesn't work with suffix versions like -release.1
  - Use exact version match instead

Why optionalDependencies:
- Installation won't fail if these packages fail to install
- Users can opt-out with: npm install foliate-js --omit=optional
- Maintains the library's "no hard dependencies" philosophy
- Graceful degradation: panel detection falls back to grid-only mode

Behavior:
- Default: npm attempts to install OpenCV, TensorFlow, COCO-SSD (~4.5MB)
- With --omit=optional: skips heavy ML/CV libraries
- Either way: library works, panel detection gracefully adapts

This resolves npm install errors where "^4.12.0" couldn't be found
because the actual version is "4.12.0-release.1".

package.json

@@ -16,8 +16,8 @@
   "exports": {
     "./*.js": "./*.js"
   },
-  "dependencies": {
-    "@techstark/opencv-js": "^4.12.0",
+  "optionalDependencies": {
+    "@techstark/opencv-js": "4.12.0-release.1",
     "@tensorflow/tfjs": "^4.22.0",
     "@tensorflow-models/coco-ssd": "^2.2.3"
   },