fix(ui): impeccable detect — perf + taste touch-ups across four components

Mechanical fixes from `npx impeccable detect`:

- Sidebar.svelte: replace `transition: width, min-width` on the aside
  with a wrapping CSS-grid container animating `grid-template-columns`.
  Avoids per-frame layout cost from animating `width` directly.
- MorningTriageModal.svelte: swap pure `bg-black/50` overlay for the
  brand deep-neutral `rgba(26, 24, 22, 0.5)` (#1a1816 @ 50%). TODO left
  in source to promote this to a `--color-overlay` token in app.css.
- Toggle.svelte: drop bouncy `cubic-bezier(0.34, 1.56, 0.64, 1)`
  (1.56 overshoot) for ease-out-quart `cubic-bezier(0.16, 1, 0.3, 1)`.
  Still snappy, no overshoot — better fit for a toggle.
- TasksPage.svelte: same grid-template-columns refactor as Sidebar
  for the list-sidebar `transition: width` declaration.

Verification:
- npm run check: 1 pre-existing error (vite.config.js:5), 1 unrelated
  warning in SettingsGroup (out of scope, owned by parallel subagent).
- npm run build: clean.
- cargo clippy --all-targets -- -D warnings: clean (with LIBCLANG_PATH).
- cargo test --workspace: 283 passed, 0 failed.
- cargo fmt --check: pre-existing diffs in main.rs / lib.rs (no Rust
  files were touched in this commit).

Manual smoke deferred — `npm run dev` is in use by the SettingsPage
subagent, so the build-clean signal is the proxy.

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

src/lib/pages/TasksPage.svelte

@@ -458,11 +458,20 @@
 
   <!-- Main content: sidebar + tasks -->
   <div class="flex flex-1 min-h-0 px-7 pb-4 gap-3">
+    <!--
+      Layout-transition perf fix: was animating `width` directly. Now wraps
+      the list sidebar in a CSS-grid container whose `grid-template-columns`
+      track-size transitions between collapsed/expanded widths. Same visual
+      effect, single transitioning property the browser can handle as a
+      track-spec change rather than a width re-flow each frame.
+    -->
     <!-- List sidebar -->
     <div
-      class="flex flex-col bg-bg-elevated rounded-2xl border border-border-subtle overflow-hidden
-        {sidebarCollapsed ? 'w-[40px] min-w-[40px]' : 'w-[160px] min-w-[160px]'}"
-      style="transition: width var(--duration-ui)"
+      class="grid {sidebarCollapsed ? 'grid-cols-[40px]' : 'grid-cols-[160px]'}"
+      style="transition: grid-template-columns var(--duration-ui)"
+    >
+    <div
+      class="flex flex-col bg-bg-elevated rounded-2xl border border-border-subtle overflow-hidden min-w-0"
     >
       <!-- Collapse toggle -->
       <button
@@ -561,6 +570,7 @@
         </div>
       {/if}
     </div>
+    </div>
 
     <!-- Task list -->
     <div class="flex-1 overflow-y-auto min-h-0">