fix(cli): harden extension registration and discovery workflows (#2499)

* chore: update community catalog with latest extension versions

- Update memory-md from 0.7.9 to 0.8.0
- Update architecture-guard from 1.6.7 to 1.8.0

* fix(cli): harden extension registration with project-level tracking in extensions.yml

* test(cli): add comprehensive unit tests for extension registration logic

* chore: remove out-of-scope catalog changes

* refactor: address PR feedback for extension registration hardening

* fix: harden extension registration defensive logic and add comprehensive unregister_hooks tests

- Add dict guard to register_hooks() to handle corrupted extensions.yml (non-dict root)
- Add 5 comprehensive tests for unregister_hooks() workflow:
  * Full workflow with hooks + installed list removal
  * Resilience when config has no 'hooks' key
  * Corrupted YAML handling
  * Multiple extension scenarios
  * All 11 tests passing

* fix: sanitize installed to strings, guard unregister_hooks dict, handle null hook values

- register_extension(): filter non-string entries from installed before sort
- register_hooks(): normalize hooks to {} when missing or not a dict
- unregister_hooks(): add isinstance(config, dict) guard before key checks
- unregister_hooks(): coerce null/scalar hook lists to [] before iteration
- tests: add 3 regression tests for no-hooks manifest, mixed-type installed, null hook values
- All 14 tests passing

* fix(cli): persist sanitization results and harden hook registration

* Harden extension registration to always persist sanitization results

* Hardening extension registration: support mapping entries, improve persistence, and fix update rollback

* fix(cli): harden extension update and unregistration workflows

* fix(cli): move update sentinels outside try block to prevent NameError on rollback

* fix(cli): sanitize hook event lists in register_hooks to prevent crashes

* fix(cli): deduplicate hook entries and harden rollback hooks-restore guards

* test(cli): add regression tests for extension update and rollback hardening

* fix(cli): deduplicate installed list by id in register_extension

* fix(cli): consolidate and harden extension update rollback logic

* fix(cli): initialize backup_registry_entry before try block to prevent UnboundLocalError on rollback

* fix(tests): return Path from download_extension mock and add Path import

* fix(cli): normalize get_project_config() return to dict; deduplicate in unregister_extension()

* fix(cli): normalize hooks/installed/settings in get_project_config(); use tmp_path-scoped zip in tests

* fix(cli): set modified=True on hook coercion in rollback; sanitize hook event values in get_project_config(); harden test assertions

* fix(cli): filter non-dict hook entries in get_project_config(); remove dead MISSING sentinel

* fix(cli): gate extensions.yml rollback on backup_hooks is not None; update stale comment

* fix(cli): move _AgentReg import outside try block; assert result.exception is None in tests

* fix(extensions): consistent key order in default config; deep-copy backup_installed

* test: fix misleading comment; assert exit_code==1 in rollback test

* test: clean up duplicate imports in hardening tests

* refactor(extensions): extract _sanitize_installed_list helper; strengthen hook unregister assertion

* fix(extensions): validate extension IDs in _sanitize_installed_list; clarify test comment