fix(docs): Update broken URLs, deprecations, and outdated references

- Replace docs.anthropic.com URLs with code.claude.com equivalents across all files
- Mark /review as deprecated with code-review plugin recommendation
- Fix "Sonnet 4.5" → "Sonnet 4.6" model name reference
- Update Task() → Agent() syntax in subagents documentation
- Remove undocumented /todos from slash commands table
- Add verification note about CLAUDE.local.md not in official docs

.github/ISSUE_TEMPLATE/config.yml

@@ -1,7 +1,7 @@
 blank_issues_enabled: false
 contact_links:
   - name: Claude Code Documentation
-    url: https://docs.anthropic.com/en/docs/claude-code
+    url: https://code.claude.com/docs/en/overview
     about: Official Claude Code documentation
   - name: Discussions
     url: https://github.com/luongnv89/claude-howto/discussions