Add modular/optional feature packs and on-demand component installer for Video & Audio

[spelech]

Introduces modular, separately installable feature packs for Video Generation (video-generation) and Audio TTS (audio-tts).

Key changes:

• Updated Inno Setup installer.iss with [Components] (core, ext_video, ext_audio) and [Types] (full, compact, custom).
• Added --with-video and --with-audio opt-in flags to install.ps1 and install_linux.sh.
• Refactored setup_ai_tools.ps1 into discrete tasks Install-VideoPack and Install-AudioPack.
• Implemented IComponentManagerService & ComponentManagerService to query, install, and uninstall optional feature packs.
• Added REST endpoints GET /api/components, POST /api/components/install (with SSE progress stream), and POST /api/components/uninstall.
• Created FeaturePackBannerControl UI banner control and integrated missing pack banners into EngineStudioTabControl.
• Added "Installed Components & Add-ons" section with disk usage status and toggles in SettingsTabControl.
• Added unit & integration tests in ComponentManagerAndEndpointsTests.cs.

Fixes #15

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PR created automatically by Jules for task 454266730511521674 started by @spelech

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