style: Fix 411 ruff lint issues (Kimi's issue #4)

Auto-fixed lint issues with ruff --fix and --unsafe-fixes:

Issue #4: Ruff Lint Issues
- Before: 447 errors (originally reported as ~5,500)
- After: 55 errors remaining
- Fixed: 411 errors (92% reduction)

Auto-fixes applied:
- 156 UP006: List/Dict → list/dict (PEP 585)
- 63 UP045: Optional[X] → X | None (PEP 604)
- 52 F401: Removed unused imports
- 52 UP035: Fixed deprecated imports
- 34 E712: True/False comparisons → not/bool()
- 17 F841: Removed unused variables
- Plus 37 other auto-fixable issues

Remaining 55 errors (non-critical):
- 39 B904: Exception chaining (best practice)
- 5 F401: Unused imports (edge cases)
- 3 SIM105: Could use contextlib.suppress
- 8 other minor style issues

These remaining issues are code quality improvements, not critical bugs.

Result: Code quality significantly improved (92% of linting issues resolved)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/skill_seekers/sync/notifier.py

@@ -4,7 +4,6 @@ Notification system for sync events.
 
 import os
 import requests
-from typing import Optional, List
 from .models import WebhookPayload
 
 
@@ -32,9 +31,9 @@ class Notifier:
 
     def __init__(
         self,
-        webhook_url: Optional[str] = None,
-        slack_webhook: Optional[str] = None,
-        email_recipients: Optional[List[str]] = None,
+        webhook_url: str | None = None,
+        slack_webhook: str | None = None,
+        email_recipients: list[str] | None = None,
         console: bool = True
     ):
         """