feat(speech): add whisper.cpp with Vulkan support for GPU acceleration (#179)

* feat(speech): add whisper.cpp with Vulkan support for GPU acceleration

Add whisper.cpp as a new speech recognition engine with the following features:
- Vulkan GPU acceleration support (AMD, Intel, NVIDIA)
- Fallback to CUDA for NVIDIA GPUs
- CPU-only mode with automatic thread optimization
- Support for all model sizes: tiny, base, small, medium, large
- Hardware detection to recommend best model/backend
- Models downloaded from Hugging Face (ggml format)
- Updated UI to show compute backend info in settings
- pywhispercpp as the Python binding library
- whisper_cpp as the new default engine

Changes:
- New whispercpp_model_info.py with model metadata and hardware detection
- Updated recognition_manager.py with whisper.cpp init and transcription
- Updated settings_dialog.py with whisper.cpp UI support
- Updated config_manager.py with whisper_cpp_model_size config
- Updated main.py with whisper_cpp CLI option
- Updated pyproject.toml with pywhispercpp dependency
- Updated install.sh with vulkan-tools for GPU detection

Closes #104

* style: fix black and isort formatting issues

* test: update config manager test for whisper_cpp default engine

* feat(install): interactive mode with 3 engine choices and whisper.cpp as default

Major changes to install.sh:
- Interactive mode is now the DEFAULT (not --auto)
- Added --auto flag for non-interactive automatic installation
- New --engine flag to specify engine directly
- Interactive mode shows 3 engine options with visual boxes:
  1. whisper.cpp (recommended) - Vulkan/CUDA/CPU support
  2. whisper (OpenAI) - PyTorch-based, NVIDIA-only
  3. VOSK - lightweight option
- Hardware detection with recommendations:
  - Detects Vulkan support (AMD/Intel/NVIDIA)
  - Detects NVIDIA CUDA
  - Checks available RAM
  - Recommends best engine based on hardware
- Updated help text with new options and examples
- Removed old --with-whisper, --whisper-cpu, --no-whisper flags
- whisper.cpp is now the default engine for automatic mode

* feat(uninstall): kill running vocalinux processes before uninstall

* fix(whisper.cpp): auto-download model, use all CPU cores, hide unavailable engines

Three fixes for whisper.cpp implementation:

1. Auto-download model during install
   - Added install_whispercpp_model() function to install.sh
   - Downloads ggml-tiny.bin (~39MB) from Hugging Face
   - Runs automatically when whisper.cpp engine is selected

2. Use all CPU cores for transcription
   - Added n_threads parameter to Model initialization
   - Uses multiprocessing.cpu_count() to get all cores
   - Significantly improves transcription speed

3. Hide unavailable engines from dropdown
   - Added get_available_engines() function to detect installed engines
   - Settings dialog now only shows engines that are actually installed
   - Falls back to first available engine if current not available

Fixes user-reported issues with whisper.cpp integration.

* ui(settings): display whisper.cpp correctly and increase dialog height

- Changed engine display name from 'whisper_cpp' to 'whisper.cpp'
- Added format_engine_display_name() helper function
- Dialog now uses 75% of screen height for better visibility
- More options visible by default without scrolling

* revert(settings): remove display name change, keep dialog height increase

- Reverted engine display name change (was breaking engine selection)
- Kept dialog height at 75% of screen for better visibility

* style: fix black and isort formatting for whisper.cpp logging

* style: fix black formatting in settings_dialog.py

* ci: fix Fedora 39 container package installation

Add dnf cache update and fallback with --nogpgcheck for Fedora containers
that may have stale or missing package metadata.

.github/workflows/distro-test-matrix.yml

@@ -35,7 +35,13 @@ jobs:
             apt-get update
             apt-get install -y bash curl python3 git
           elif command -v dnf >/dev/null 2>&1; then
-            dnf install -y bash curl python3 git
+            # Fedora needs cache update first in container environment
+            dnf clean all || true
+            dnf makecache || true
+            dnf install -y bash curl python3 git || {
+              echo "⚠ dnf install failed, trying with --nogpgcheck..."
+              dnf install -y --nogpgcheck bash curl python3 git
+            }
           fi
 
       # ============================================================================