Feature gui improvements

[joenaess]

Description

This PR introduces a few GUI features to the easysearch web interface to hopefully improve the productivity of users reviewing transcripts.

Key Additions

1. Playback Speed Controls

• Added a responsive <select> dropdown next to the audio player in the UI.
• Allows users to precisely adjust audio transcription playback speed from 0.5x up to 2.0x.
• Stays perfectly synchronized with the requestAnimationFrame word-level highlighting.

2. Global Keyboard Navigation

• Added keydown event listeners to the global context to allow power-user keyboard navigation holding the interface:
  • Spacebar: Toggles Play/Pause globally, regardless of where the mouse cursor is located (unless typing in the search bar).
  • ArrowLeft / ArrowRight: Skips the audio backwards and forwards precisely by 5-second intervals.

3. Native VTT Subtitle Export

• Implemented a purely client-side export utility that downloads the current transcript directly from the page view state without hitting the backend server.
• Clicking the "Download VTT" button dynamically parses the easysearch alignment data and formats it into standard timeline syntax for a .vtt (Video Text Track) file, triggering an instant browser-native download.

Documentation

• Updated docs/get-started/search.qmd to detail these new "Advanced Player Controls".

Verification

• Features were successfully verified on a local instance using test.wav alignment outputs.
• UI elements adapt properly to the pre-existing system dark mode in style.css.

[joenaess]

Hoppas det är användbart ;-)