hls: remove legacy /video/stream + /video/{path} routes

The hash-keyed `/video/hls/{hash}/{file}` route fully covers HLS
playback now and both clients (Apollo, FileViewer-React) have
shipped updates that use it directly. Keeping the basename-keyed
fallback only encouraged stale URLs to keep flowing — every legacy
file was deleted by the startup migration, so the routes were
guaranteed 404 machines.

Dropped:
- `stream_video` handler (`GET /video/stream?path=…`) — the original
  basename-keyed playlist serve.
- `get_video_part` handler (`GET /video/{path}`) — bare-filename
  segment serve. The new layout's segments live in
  `<shard>/<hash>/segment_NNN.ts` and reach the client via
  `stream_hls_file`.
- `legacy_path` field on `GenerateVideoResponse` (serialised as
  `playlist`). The field always pointed at a file the migration had
  deleted; current clients ignore it entirely.
- Their service registrations in `main.rs`.
- The body-side `filename` extraction in `generate_video` (existed
  only to construct `legacy_path`) and the now-unused `global`
  opentelemetry import in `handlers/video.rs`.

All 707 tests still pass. Same hand-rolled validators (`is_valid_hash`
/ `is_allowed_hls_filename`) keep the new route's defense-in-depth
intact.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/main.rs

@@ -284,11 +284,9 @@ fn main() -> std::io::Result<()> {
                 .service(handlers::image::get_image)
                 .service(handlers::image::upload_image)
                 .service(handlers::video::generate_video)
-                .service(handlers::video::stream_video)
                 .service(handlers::video::stream_hls_file)
                 .service(handlers::video::get_video_preview)
                 .service(handlers::video::get_preview_status)
-                .service(handlers::video::get_video_part)
                 .service(hls_stats::hls_stats_handler)
                 .service(handlers::favorites::favorites)
                 .service(handlers::favorites::put_add_favorite)