WebSocket job progress + mobile-responsive web UI

WebSocket progress
- New `/ws/progress` route using axum 0.7's `ws` feature. Upgrades to
  a WebSocket that streams the same `ProgressResponse` payload as the
  HTTP polling endpoint, pushed instantly whenever a job moves.
- `WebState.progress_tx` is a `tokio::sync::broadcast::Sender<String>`
  (capacity 16, lossy — Lagged subscribers resync on the next tick).
- A background tokio task ticks every 500 ms while any download is
  running or queued, every 5 s when idle. Skips the JSON encode when
  no subscribers are listening, so a single-user install pays zero
  CPU for the broadcast when the browser tab is closed.
- JS replaces the per-interval HTTP poll with a WebSocket connection.
  The polling path stays as fallback for mobile carriers / reverse
  proxies that strip WS — when the socket closes or fails to open,
  schedulePoll() resumes immediately and a reconnect attempt fires
  after 5 s.
- Initial snapshot is sent right after subscribe so the UI is live
  before the next tick.

Mobile-responsive web UI
- Existing `@media(max-width:640px)` block tightened:
  - Hide the H1, AGPL footer notice, sort dropdown, and library-size
    counter — they don't fit and aren't actionable.
  - Header buttons get min 34×34 hit targets (Apple HIG / Material).
  - `.card-foot` wraps and grows to 34×34 buttons so the five action
    icons (play / watched / favourite / bookmark / waiting) stay
    tappable instead of cramming into thumb-unfriendly 22 px chips.
  - Modals go full-screen (no 10 px page-margin) so the iPhone safe
    area doesn't crop content.
  - Footer (URL bar + download button) wraps onto two rows so neither
    squeezes the other off-screen.
  - Bulk-actions toolbar wraps and gets bigger buttons.
  - Per-job stdout preview hides on small screens.
- New `@media(max-width:380px)` collapses the grid to single column
  for very narrow phones.

55 unit tests still pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Cargo.toml

@@ -14,7 +14,7 @@ rusqlite = { version = "0.31", features = ["bundled"] }
 r2d2 = "0.8"
 r2d2_sqlite = "0.24"
 notify-rust = { version = "4", default-features = false, features = ["z"] }
-axum = { version = "0.7", features = ["macros"] }
+axum = { version = "0.7", features = ["macros", "ws"] }
 tokio = { version = "1", features = ["full"] }
 tokio-util = { version = "0.7", features = ["io"] }
 tokio-stream = "0.1"