refactor: systematic code quality improvements across 20 dimensions (#377)

* refactor: improve code quality across multiple dimensions

Code quality improvements identified and driven by desloppify analysis:

**action_handler.py**
- Replace 9 repetitive shortcut forwarding methods with data-driven
  _SHORTCUT_ACTIONS class-level dispatch table
- Add _make_shortcut_handler() factory for shortcut closures
- Add explicit type annotation for action_handlers dict

**config_manager.py**
- Move 'import copy' from __init__ to module level (stdlib best practice)
- Add _VALID_SECTIONS frozenset for section name validation in set()
- Narrow broad Exception catch to (KeyError, TypeError) in set()
- Add deprecation warning to save_settings() guiding toward save_config()

**tray_indicator.py**
- Consolidate all imports at module top level
- Remove noqa E402 suppressions for mid-file imports
- Move ResourceManager import alongside other local imports

**recognition_manager.py**
- Narrow broad 'except Exception' to 'except OSError' for audio device
  enumeration errors
- Narrow 'except Exception' to 'except (FileNotFoundError, OSError)' for
  notification subprocess errors

**Tests**
- Update test assertions to use specific exception types matching narrowed
  catches (OSError, FileNotFoundError instead of Exception/RuntimeError)

* refactor: improve type safety, callback contracts, and method decomposition

**main.py** — Mid-level elegance
- Document callback wiring contract: text_callback, action_callback,
  state_callback with threading context, argument types, and behavior
- Add return type annotations to nested callback functions
- Reorder: define callbacks before registration for readability

**config_manager.py** — Type safety, error consistency
- Add typed accessors: get_str(), get_bool(), get_int(), get_float(),
  get_optional_int() eliminating Any returns for common access patterns
- Narrow load_config exception to (json.JSONDecodeError, OSError)
- Narrow save_config exception to (OSError, TypeError)

**recognition_manager.py** — Low-level elegance
- Decompose _init_whispercpp (141 lines) into three focused methods:
  - _init_whispercpp: validation and download gating (35 lines)
  - _load_whispercpp_model: backend detection and model loading (55 lines)
  - _handle_gpu_fallback: GPU incompatibility recovery (40 lines)
- Narrow exception catch from broad Exception to specific types

**tray_indicator.py, settings_dialog.py** — Type safety
- Migrate config access from untyped get() to typed get_str(),
  get_bool(), get_optional_int() across 8 call sites

* refactor: narrow 11 more broad Exception catches to specific types

Systematically replaced broad 'except Exception' with specific exception
types across recognition_manager.py:

- test_audio_input: (OSError, ValueError) for audio read errors
- test_audio_input outer: (OSError, ValueError, RuntimeError) for unexpected
- _init_whisper: (RuntimeError, OSError) for engine init failures
- _transcribe_with_whisper: (RuntimeError, OSError, ValueError) for transcription
- _download_whispercpp_model: (OSError, RuntimeError, ValueError) for downloads
- _download_vosk_model: (OSError, RuntimeError, ValueError) for downloads
- _download_whisper_model: (OSError, RuntimeError, ValueError) for downloads

This brings the total narrowed exception catches to 18+ across the codebase,
improving error consistency and making failure modes more predictable.

* style: fix black formatting issues

Auto-format with black to fix CI lint failures in recognition_manager.py,
settings_dialog.py, and test_settings_shortcuts.py.

* test: add coverage for typed config accessors

Add TestTypedAccessors class with 15 tests covering:
- get_str(): string values, defaults, non-string conversion, None handling
- get_bool(): boolean values, defaults
- get_int(): integer values, invalid input fallback, missing key defaults
- get_float(): float values, invalid input fallback
- get_optional_int(): int values, None values, missing keys, invalid input

Fixes codecov/patch coverage requirement for new typed accessor methods.

tests/test_recognition_manager_init.py

@@ -177,13 +177,14 @@ class TestGetAudioInputDevices:
                 assert devices == []
 
     def test_get_audio_input_devices_generic_exception(self):
-        """Test handling of generic exceptions during device enumeration."""
+        """Test handling of OS-level audio errors during device enumeration."""
         from vocalinux.speech_recognition.recognition_manager import get_audio_input_devices
 
-        with patch.dict("sys.modules", {"pyaudio": MagicMock()}):
-            with patch("builtins.__import__", side_effect=RuntimeError("Unexpected error")):
-                devices = get_audio_input_devices()
-                assert devices == []
+        mock_pyaudio = MagicMock()
+        mock_pyaudio.PyAudio.side_effect = OSError("Audio subsystem error")
+        with patch.dict("sys.modules", {"pyaudio": mock_pyaudio}):
+            devices = get_audio_input_devices()
+            assert devices == []
 
 
 class TestGetSupportedChannels: