feat: update all Docker Compose files for Vision primary with WIF auth (refs #127)

- Switch OCR engine config to google_vision primary / paddleocr fallback
- Mount Auth0 OCR secrets and WIF config into all OCR containers
- Add WIF config to repo (not a secret, contains no credentials)
- Remove obsolete google-vision-key.json.example

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

secrets/app/google-wif-config.json

@@ -0,0 +1,14 @@
+{
+  "universe_domain": "googleapis.com",
+  "type": "external_account",
+  "audience": "//iam.googleapis.com/projects/487954699429/locations/global/workloadIdentityPools/motovaultpro-pool/providers/auth0-provider",
+  "subject_token_type": "urn:ietf:params:oauth:token-type:jwt",
+  "token_url": "https://sts.googleapis.com/v1/token",
+  "credential_source": {
+    "executable": {
+      "command": "/app/scripts/fetch-auth0-token.sh",
+      "timeout_millis": 30000
+    }
+  },
+  "service_account_impersonation_url": "https://iamcredentials.googleapis.com/v1/projects/-/serviceAccounts/mvp-svc-account@motovaultpro.iam.gserviceaccount.com:generateAccessToken"
+}