Add URL-based transcript range slicing for insert and side-panel flows

[Copilot]

Users currently have to fetch full transcripts and manually trim content, which is cumbersome for long videos. This change adds first-class support for requesting only a specific segment (e.g. 2:48 to 7:59) directly from the YouTube URL.

• Time-range parsing from YouTube URLs

  • Added extractYouTubeTimeRange(url) in src/youtube/url.ts.
  • Supports start, end, t, and #t= inputs with common formats (mm:ss, hh:mm:ss, 2m48s, raw seconds).
  • Normalizes to millisecond bounds and drops invalid end bounds (end <= start).

• Transcript line range filtering

  • Added filterTranscriptLinesByRange(...) in src/transcript/range.ts.
  • Uses overlap semantics so lines intersecting the requested window are retained.

• Applied to both transcript output paths

  • src/transcript/format.ts: insert command output is now range-aware.
  • src/obsidian/views/transcript-view.ts: side-panel rendering is now range-aware.
  • Side-panel timestamp links now use buildTimestampUrl(...) for consistent URL handling.

• User-facing docs update

  • README now documents segment usage via URL parameters for both workflows.

const url =
  "https://www.youtube.com/watch?v=dQw4w9WgXcQ&start=2:48&end=7:59";

const range = extractYouTubeTimeRange(url);
// { startMs: 168000, endMs: 479000 }

const linesInRange = filterTranscriptLinesByRange(transcript.lines, range);