Clean up stale comments, dead code, and code quality issues

- Remove dead code: unused PENDING_FILE, _extract_domain(), sender_domain
  field, imap_uid fallback, check_unseen_only config key
- Fix stale comments: removed tag references in README and docstrings,
  top_domains -> top_senders, 1-based number -> scan_index number
- Make _extract_email_address public (used by 3 modules)
- Extract _format_address helper to deduplicate from/to parsing
- Batch pending queue disk I/O in review act/accept (load once, save once)
- Reuse cleared pending dict in scan instead of redundant disk load
- Track envelope IDs during scan loop to catch duplicates
- Fix default confidence_threshold 75 -> 85 to match config and docs
- Update get_relevant_examples default n=10 -> n=5 to match caller
- Add graceful error for --recent with non-numeric value

scripts/email_processor/config.json

@@ -4,8 +4,7 @@
     "model": "kamekichi128/qwen3-4b-instruct-2507:latest"
   },
   "rules": {
-    "max_body_length": 1000,
-    "check_unseen_only": true
+    "max_body_length": 1000
   },
   "automation": {
     "confidence_threshold": 85