fix: more corner-case audit — partial-failure UX + defensive parsing

Three small reliability fixes from re-auditing:

1. Playlist.vue used Promise.all, so a flaky /detail endpoint would
   blank out the whole page even though /songs returned just fine.
   Switch to allSettled and synthesize a stub playlist header from
   the song list when only detail fails. User can still play the
   playlist; just loses the description/cover.

2. sourceTabs.readAll: typeof null === 'object' AND typeof [] ===
   'object', so a corrupted localStorage value (e.g. an array) would
   be treated as a record and its missing keys would silently fall
   back. Reject explicitly so the failure mode is "clean defaults"
   instead of "wrong shape that almost works".

3. Settings.vue loadProfileConfig: a 200 response with empty/wrong
   body would set profileConfigs[botId] to a falsy/wrong-shape value,
   leaving the row stuck on "加载中..." (because the v-if uses
   !profileConfigs[id]). Validate the shape; surface "响应格式异常"
   so the retry link is reachable.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/src/stores/sourceTabs.ts

@@ -13,7 +13,13 @@ function readAll(): Partial<Record<TabKey, Source>> {
     const raw = localStorage.getItem(STORAGE_KEY);
     if (!raw) return {};
     const parsed = JSON.parse(raw);
-    return typeof parsed === 'object' && parsed !== null ? parsed : {};
+    // typeof null === 'object' and typeof [] === 'object' — both pass a
+    // naive check but neither is a valid record. Reject explicitly so a
+    // corrupted / manipulated value can't smuggle wrong shapes through.
+    if (parsed === null || typeof parsed !== 'object' || Array.isArray(parsed)) {
+      return {};
+    }
+    return parsed as Partial<Record<TabKey, Source>>;
   } catch {
     return {};
   }