ci: mypy ratchet -- keep type-clean modules clean (71 modules, 536 -> 442 errors) (#661)

* ci: mypy ratchet -- keep type-clean modules clean

mypy-clean.txt lists the 71 modules under src/ that type-check clean;
scripts/check_types.py runs mypy (--follow-imports=silent) on exactly
those files and fails on any error or a missing/unsorted/duplicate entry.
A new "Type check (mypy ratchet)" CI job runs it with mypy 1.20.2 and
pinned stubs; the manual pre-commit mypy hook now runs the same script
(a local hook, so mypy sees the installed requirements like CI does).

35 modules were made clean with annotation-only fixes: hints, typing.cast,
TYPE_CHECKING imports, implicit-Optional defaults made explicit, and
annotations widened (never guards removed) where mypy called a defensive
isinstance check unreachable. No runtime behaviour change.

mypy.ini: numpy and orjson are treated as Any (follow_imports=skip, also
for stubs). numpy 2.3+ stubs use 3.12 `type` statements that mypy won't
parse at python_version 3.10, and orjson is optional, so seeing its stubs
made the result depend on whether it was installed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* chore: annotate check_types.py's list-form mypy subprocess

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

src/plugin_system/saved_repositories.py

@@ -7,7 +7,7 @@ Manages saved GitHub repository URLs for easy plugin discovery and installation.
 import json
 import os
 from pathlib import Path
-from typing import List, Dict, Optional
+from typing import List, Dict, Optional, cast
 
 from src.logging_config import get_logger
 from src.plugin_system.repo_urls import normalize_repo_url
@@ -37,7 +37,7 @@ class SavedRepositoriesManager:
                     if isinstance(data, list):
                         return data
                     elif isinstance(data, dict) and 'repositories' in data:
-                        return data['repositories']
+                        return cast(List[Dict[str, str]], data['repositories'])
                     else:
                         return []
             return []