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/components/MorningTriageModal.svelte

@@ -257,9 +257,15 @@
 <svelte:window onkeydown={handleKeydown} />
 
 {#if open}
+  <!--
+    Pure-black-white taste fix: replaced `bg-black/50` overlay with the brand
+    deep-neutral `#1a1816` at 50% alpha. TODO: promote this colour to a
+    `--color-overlay` token in app.css so the value isn't inlined per-modal.
+  -->
   <div
     bind:this={dialogEl}
-    class="fixed inset-0 z-50 flex items-center justify-center bg-black/50 backdrop-blur-sm animate-fade-in"
+    class="fixed inset-0 z-50 flex items-center justify-center backdrop-blur-sm animate-fade-in"
+    style="background: rgba(26, 24, 22, 0.5)"
     role="dialog"
     aria-modal="true"
     aria-labelledby="triage-title"