fix(web): task launcher textarea no longer grows while typing; less transparent windows on Firefox

The launcher's textarea inherited the base Textarea component's default
field-sizing:content (auto-grow to fit typed content) — ChatThread's
input already overrides this with field-sizing-fixed, but the desktop
launcher never did, so the box would jump taller the moment you started
typing. Also bumps the floating-window frosted-glass opacity from 70%
to 85%: backdrop-filter's blur strength isn't consistent across
engines, and Firefox blurs noticeably less than Chromium at the same
radius, making the Chromium-tuned opacity look far too see-through
there.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

web/src/lib/components/desktop-shell/TaskLauncher.svelte

@@ -50,7 +50,7 @@
       onkeydown={handleKeydown}
       placeholder="e.g. Roll the staging database back to last night's snapshot and verify the app is healthy…"
       rows={compact ? 2 : 3}
-      class="max-h-52 min-h-24 resize-none border-0 bg-transparent px-4 py-3.5 text-base shadow-none focus-visible:ring-0"
+      class="max-h-52 min-h-24 resize-none field-sizing-fixed border-0 bg-transparent px-4 py-3.5 text-base shadow-none focus-visible:ring-0"
     />
     <div class="flex items-center justify-between px-3 pb-3">
       <span class="text-[11px] text-muted-foreground">Enter to start · Shift+Enter for newline</span>