feat: integrate Google Scholar alerts and improve paper filtering pipeline

- Add Google Scholar Alert collection via Gmail IMAP
- Add Gmail App Password based authentication
- Add Google Scholar environment variables to NAS compose configuration
- Enable Google Scholar Alert source in config.nas.yaml
- Disable subject filtering that incorrectly excluded Scholar alert emails
- Parse paper titles and links from Google Scholar alert HTML emails
- Deduplicate collected Scholar papers by normalized title
- Filter Scholar UI/control links such as update alert and unsubscribe entries
- Filter bracket-only alert labels such as [automotive radar]

- Add Google Scholar specific relevance threshold
- Keep global min_relevance at 2
- Set Google Scholar minimum relevance to 3
- Reduce Scholar candidates from 229 collected / 207 merged to 28 accepted

- Add Gemini API rate limiting
- Enforce minimum 13 second interval between Gemini requests
- Apply shared rate limiter to abstract and full-text enrichment
- Prevent Gemini free-tier 5 RPM quota errors
- Verify retry processing of previously failed AI enrichment jobs

- Verify end-to-end NAS workflow
- Google Scholar Alert collection successful
- Gemini enrichment successful without HTTP 429 errors
- Joplin report generation and WebDAV synchronization successful

state/provider_circuit_breaker_state.json

@@ -5,5 +5,12 @@
     "strikes": {
       "http_403": 1
     }
+  },
+  "crossref": {
+    "open_until": 1787231271.0746372,
+    "reason": "network_error",
+    "strikes": {
+      "network_error": 1
+    }
   }
 }