feat(anime): filter episodes and mark them watched by hand

- Add a filter box above the episode list for a number, range, or name substring, with a "N of M" counter
- Read watch marks from the immersion tracker stats and show them per episode, with a watched count in the header, refreshed on window focus
- Add a right-click menu to mark one episode or a whole catch-up span (this and everything below) watched/unwatched
- Add setWatched/getWatchState IPC plumbing so a manual mark creates the stats row for an episode that was never played

src/animeui/episode-filter.test.ts

@@ -0,0 +1,61 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { filterEpisodes, parseEpisodeFilter } from './episode-filter';
+
+const episode = (number: number | null, name: string) => ({ number, name });
+
+const SEASON = [
+  episode(1, 'Episode 1 - Departure'),
+  episode(2, 'Episode 2 - The Long Road'),
+  episode(12, 'Episode 12 - Homecoming'),
+  episode(12.5, 'Episode 12.5 - Recap'),
+  episode(18, 'Episode 18 - Finale'),
+  episode(null, 'OVA: Beach Special'),
+];
+
+test('an empty query keeps the whole list', () => {
+  assert.deepEqual(filterEpisodes(SEASON, '   '), SEASON);
+  assert.equal(parseEpisodeFilter(''), null);
+});
+
+test('a number matches that episode, not every episode containing the digits', () => {
+  assert.deepEqual(
+    filterEpisodes(SEASON, '12').map((item) => item.number),
+    [12, 12.5],
+  );
+});
+
+test('a number still matches names when the source reported no numbers', () => {
+  const unnumbered = [episode(null, 'Episode 3'), episode(null, 'Episode 4')];
+  assert.deepEqual(
+    filterEpisodes(unnumbered, '3').map((item) => item.name),
+    ['Episode 3'],
+  );
+});
+
+test('a range keeps the episodes inside it, in either order', () => {
+  assert.deepEqual(
+    filterEpisodes(SEASON, '12-18').map((item) => item.number),
+    [12, 12.5, 18],
+  );
+  assert.deepEqual(
+    filterEpisodes(SEASON, '18 – 12').map((item) => item.number),
+    [12, 12.5, 18],
+  );
+});
+
+test('a range skips episodes the source gave no number', () => {
+  assert.deepEqual(filterEpisodes([episode(null, 'OVA')], '1-99'), []);
+});
+
+test('anything else is a case-insensitive substring of the name', () => {
+  assert.deepEqual(
+    filterEpisodes(SEASON, 'home').map((item) => item.number),
+    [12],
+  );
+  assert.deepEqual(
+    filterEpisodes(SEASON, 'BEACH').map((item) => item.name),
+    ['OVA: Beach Special'],
+  );
+  assert.deepEqual(filterEpisodes(SEASON, 'nothing here'), []);
+});