Remember and restore last playback position per video

Saves playback position to store on pause and periodically every
10s during playback. Restores position (>1s) when the same video
is loaded again, showing a 'Resumed from 0:42' toast.

Files:
- frontend/app.js: resumePositions in data, save in pause/timeupdate,
  restore in Player.afterLoad, boot merge includes resumePositions

BACKLOG.md

@@ -19,7 +19,7 @@ bottom as they come up.
 - [x] Loading skeletons for search results instead of a bare "Searching…".
 - [x] Keyboard-shortcut help overlay (press `?`), listing space / arrows / f / m.
 - [x] Download/preload progress indicator on cards (percent or a bar, not just a pulse).
-- [ ] Remember and restore the last playback position per video.
+- [x] Remember and restore the last playback position per video.
 - [ ] Toast queue (stack multiple toasts instead of replacing).
 
 ## Features

frontend/app.js

@@ -45,7 +45,7 @@ function toAssetUrl(path) {
 }
 
 // ---------- State ----------
-let data = { playlists: [], history: [], settings: { quality: 'auto', volume: 1, audioOnly: false, autoPreload: true } };
+let data = { playlists: [], history: [], settings: { quality: 'auto', volume: 1, audioOnly: false, autoPreload: true }, resumePositions: {} };
 let view = { type: 'search' };          // 'search' | 'history' | 'playlist' | 'settings'
 let searchResults = [];
 let queue = [];                          // list of video objects for autoplay
@@ -245,6 +245,19 @@ const Player = {
     els.npChannel.textContent = current.meta.channel || '';
     updateNowPlayingActions();
     markPlayingCard();
+    // Restore saved playback position
+    const id = current.meta.id;
+    if (data.resumePositions[id] && data.resumePositions[id] > 1) {
+      const saved = data.resumePositions[id];
+      const restore = () => {
+        Player.seek(saved);
+        toast('Resumed from ' + fmtTime(saved));
+        Player.master.removeEventListener('canplay', restore);
+        Player.master.removeEventListener('loadedmetadata', restore);
+      };
+      Player.master.addEventListener('canplay', restore, { once: true });
+      Player.master.addEventListener('loadedmetadata', restore, { once: true });
+    }
   },
 
   // Ordered list of qualities to try if playback errors out. Progressive
@@ -459,7 +472,28 @@ function wirePlayerEvents() {
     el.addEventListener('waiting', () => { if (masterIs(el)) { showSpinner(true); if (Player.secondary) Player.secondary.pause(); } });
     el.addEventListener('playing', () => { if (masterIs(el)) { showSpinner(false); if (Player.secondary && !el.paused) { Player.secondary.currentTime = el.currentTime; Player.secondary.play().catch(() => {}); } } });
     el.addEventListener('canplay', () => { if (masterIs(el)) showSpinner(false); });
-    el.addEventListener('timeupdate', () => { if (masterIs(el)) updateProgress(); });
+    el.addEventListener('timeupdate', () => {
+      if (masterIs(el)) {
+        updateProgress();
+        // Persist playback position every 10s
+        if (current && current.meta) {
+          const t = Player.master.currentTime;
+          if (t > 5 && Math.floor(t) % 10 === 0) {
+            data.resumePositions[current.meta.id] = t;
+            persist();
+          }
+        }
+      }
+    });
+    el.addEventListener('pause', () => {
+      if (masterIs(el) && current && current.meta) {
+        const t = Player.master.currentTime;
+        if (t > 1) {
+          data.resumePositions[current.meta.id] = t;
+          persist();
+        }
+      }
+    });
     el.addEventListener('loadedmetadata', () => { if (masterIs(el)) updateProgress(); });
     el.addEventListener('ended', () => { if (masterIs(el)) playNext(); });
     el.addEventListener('error', () => {
@@ -1137,6 +1171,7 @@ async function boot() {
       data = {
         playlists: loaded.playlists || [],
         history: loaded.history || [],
+        resumePositions: loaded.resumePositions || {},
         settings: { quality: 'auto', volume: 1, audioOnly: false, autoPreload: true, ...(loaded.settings || {}) },
       };
     }