Fix M17: statusByUrl picks highest-priority status for duplicate URLs

LibraryView mapped url -> status by last-write, so when a URL had multiple
queue entries ("Download anyway"), the row reflected whichever item was
iterated last. Added a STATUS_PRIORITY ranking (completed > downloading >
queued > saved > paused > error > canceled) and keep the highest-priority
status per URL, so a row shows the most meaningful state of that video.

typecheck + 242 tests + eslint green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CODE-AUDIT.md

@@ -272,7 +272,7 @@ token system + shared primitives (UI/SIMP — high value, larger effort) · i18n
   fallback is dependency-free (no Fluent/theme provider — the crash may have come from that tree), logs via
   `componentDidCatch`, shows the error message, and offers a Reload button (`window.location.reload()`;
   persisted data lives in main, so nothing is lost).*
-- [ ] **M17 — `statusByUrl` collapses duplicate URLs.** LibraryView maps URL→status into one
+- [x] **M17 — `statusByUrl` collapses duplicate URLs.** LibraryView maps URL→status into one
   `Map`; with "Download anyway" duplicates, a row can reflect the wrong item's state.
 - [ ] **M18 — Audio "quality" presets hard-code MP3.** `QUALITY_OPTIONS.audio` labels ("Best
   (MP3)", "320 kbps") are shown even when `downloadOptions.audioFormat` is opus/flac/wav, so the