fix(web/m7-364): vitest failures — exact-match query, inert prop, -0, user guard

CI test-web was blocking on:

- QueueDrawer.test close-button query: getByLabelText(/close queue/i)
  matched BOTH the backdrop button (aria-label="Close queue backdrop")
  and the close button (aria-label="Close queue"). Switched to exact
  string match.

- QueueDrawer.test inert assertion: Svelte 5 + jsdom uses property
  binding for `inert`, not attribute, so hasAttribute('inert') returns
  false. Check the DOM property (with attribute fallback for
  robustness) instead.

- queue-row-math.ts -0 normalization: Math.round(-0.5) returns -0,
  and Object.is(-0, 0) is false — vitest's .toBe(0) fails. Added
  `|| 0` to normalize -0 to +0 at the function boundary so consumers
  never see -0.

- player/store.svelte.ts user import guard: persistence $effect.root
  reads `user.value?.id` at module-init, but in test files where
  auth/store.svelte.ts is imported transitively (auth/store.test,
  playlists/playlists.test), the player module loads via auth's
  import chain before auth's `user` binding is assigned. `user?.value`
  guards against that init-order race. The proper fix is to invert
  the auth↔player import dep (filed as I2 follow-up under #375).

web/src/lib/player/store.svelte.ts

@@ -397,7 +397,10 @@ $effect.root(() => {
   // queue/index changes drive it. The throttled-write effect below
   // covers position drift.
   $effect(() => {
-    const userId = user.value?.id;
+    // `user?.value` (not `user.value`) guards against module-init order during
+    // tests: auth/store.svelte.ts imports from this file, so when this module
+    // loads via that chain, `user` may not yet be assigned. See I2 follow-up.
+    const userId = user?.value?.id;
     if (!userId) return;
     // Reading these registers the reactive dependency; the values
     // themselves are unused — writePersistedQueue re-reads live state.
@@ -413,7 +416,7 @@ $effect.root(() => {
 
   // Throttled write on position changes.
   $effect(() => {
-    const userId = user.value?.id;
+    const userId = user?.value?.id;
     if (!userId) return;
     const _p = _position;
     void _p;