Upload date in UI; extract HTML_UI; Twitch clips mode; DB connection pool

Four nice-to-have items, plus surfacing the upload date in both UIs
since the user explicitly asked.

Upload date display
- Desktop: card meta row now includes a `YYYY-MM-DD` cell between the
  ID and the duration; detail panel header shows it as `📅 YYYY-MM-DD`.
- Web: video player modal title gains a date+duration subline so the
  viewer has context without opening the metadata pane (card meta
  already shows the date).
- New `format_upload_date()` helper on the desktop side; the web side
  reuses the existing `fmtDate()` JS.

Extract HTML_UI to include_str!
- `LOGIN_HTML` and `HTML_UI` moved out of `src/web.rs` into
  `src/web_ui/login.html` and `src/web_ui/index.html`. The Rust file
  drops from 2915 lines to 1806; editors now syntax-highlight the
  HTML/CSS/JS, and UI diffs no longer overwhelm the Rust diff view.
- `include_str!` bakes them into the binary at compile time, so there
  is no runtime fs lookup and no extra deploy artifacts.

Twitch clips-only mode
- `classify_twitch` now recognises `twitch.tv/<user>/clips` as a
  Channel URL (was Unknown), so yt-dlp's TwitchClips extractor is
  reachable from our normal download pipeline.
- Both UIs gain a "Clips only" toggle visible only when the URL is
  a Twitch channel (not a specific VOD/clip). On submit, the URL is
  rewritten to `twitch.tv/<user>/clips` before dispatch.
- 1 new platform test covers the clips-listing classification.

DB connection pool (r2d2_sqlite)
- `Database` now wraps an `r2d2`-managed SQLite pool. File-backed
  databases get up to 4 connections; the in-memory fallback is capped
  at 1 (since each in-memory connection is a fresh empty DB by default
  in SQLite).
- `WebState.db` drops its outer `Mutex` — concurrent handlers each
  check out their own connection from the pool. Static-file fetches
  through `/files/` no longer serialize on the watched/positions/
  password lookups that the auth middleware performs.
- Pool init failures are converted to `rusqlite::Error` so the
  existing `Result<T>` return types still work.

47 unit tests pass.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/platform.rs

@@ -230,9 +230,11 @@ fn classify_tiktok(url: &str) -> UrlKind {
 }
 
 fn classify_twitch(url: &str) -> UrlKind {
-    // twitch.tv/<user>           → Channel
+    // twitch.tv/<user>           → Channel (bare profile)
+    // twitch.tv/<user>/clips     → Channel (clips-only listing)
+    // twitch.tv/<user>/videos    → Channel (VOD listing)
     // twitch.tv/videos/<id>      → Video (VOD)
-    // twitch.tv/<user>/clip/<id> → Video (clip)
+    // twitch.tv/<user>/clip/<id> → Video (single clip)
     if let Some(rest) = url.split("twitch.tv/").nth(1) {
         let first = rest.split('/').next().unwrap_or("").trim_end_matches('?');
         if first.is_empty() { return UrlKind::Unknown; }
@@ -240,10 +242,16 @@ fn classify_twitch(url: &str) -> UrlKind {
         if rest.contains("/clip/") || rest.contains("/video/") {
             return UrlKind::Video;
         }
-        // No nested path means a bare channel page.
         let nested = rest.trim_start_matches(first).trim_start_matches('/');
         let nested = nested.split('?').next().unwrap_or("");
-        if nested.is_empty() || nested == "videos" || nested == "about" {
+        // Bare channel + channel-scoped listing pages all collapse to Channel.
+        // yt-dlp's extractors recognise each variant and pull the right
+        // subset (clips/highlights/uploads/all) without further hints.
+        if nested.is_empty()
+            || nested == "videos"
+            || nested == "about"
+            || nested == "clips"
+        {
             return UrlKind::Channel { handle: first.to_string() };
         }
     }
@@ -423,6 +431,15 @@ mod tests {
         assert!(matches!(info.kind, UrlKind::Video));
     }
 
+    #[test]
+    fn twitch_clips_listing_is_channel() {
+        let info = classify_url("https://www.twitch.tv/streamername/clips");
+        match info.kind {
+            UrlKind::Channel { handle } => assert_eq!(handle, "streamername"),
+            _ => panic!("expected Channel with clips listing"),
+        }
+    }
+
     #[test]
     fn vimeo_numeric_is_video() {
         let info = classify_url("https://vimeo.com/123456");