feat: Improve UI layout and navigation

- Increase logo size (48x48 desktop, 56x56 mobile) for better visibility
- Add logo as favicon
- Add logo to mobile header
- Move user menu to navigation bars (sidebar on desktop, bottom bar on mobile)
- Fix desktop chat layout - container structure prevents voice controls cutoff
- Fix mobile bottom bar - use icon-only ActionIcons instead of truncated text buttons
- Hide Create Node/New Conversation buttons on mobile to save header space
- Make fixed header and voice controls work properly with containers

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

public/logo.svg

@@ -0,0 +1,16 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 60 100" width="256" height="256" aria-labelledby="logoTitle">
+  <title id="logoTitle">Woven abstract logo of communication waves (Vertical)</title>
+
+  <g fill-rule="evenodd" fill="none" transform="translate(-18, 20) rotate(90, 48, 30) translate(0, 60) scale(1, -1)">
+
+    <!-- Jagged wave - Left end segment (draw first, appears behind) --><path stroke="#AAAAAA" stroke-width="1" stroke-linecap="round" fill="none" d="M 42 30 L 45 26.25" />
+
+    <!-- Jagged wave - Right end segment (draw second, appears behind) --><path stroke="#AAAAAA" stroke-width="1" stroke-linecap="round" fill="none" d="M 51 33.75 L 54 30" />
+
+    <!-- Curved wave (drawn third, appears in middle layer) --><path stroke="#444444" stroke-width="1" stroke-linecap="round" fill="none" d="M 42 30 Q 45 37.5, 48 30 Q 51 22.5, 54 30" />
+
+    <!-- Jagged wave - Center segment (drawn last, appears in front) --><path stroke="#AAAAAA" stroke-width="1" stroke-linecap="round" fill="none" d="M 45 26.25 L 48 30 L 51 33.75" />
+
+  </g>
+
+</svg>