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>

todo.md

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+# TODO
+
+Upcoming items that should be implemented (time-permitting):
+
+- a way to see the visualized version of all nodes in the db
+- let's call the "AI" "Mr. DJ" and link to this youtube video for its name:
+  https://www.youtube.com/watch?v=oEauWw9ZGrA
+- let's have "Ponderants" in the top-left corner with some sort of very minimal
+  svg that represents an abstraction of a human conversing with a robot (like
+  maybe four simple shapes max)
+- let's have, in the top-center, something that indicates we're in "Convo" mode
+- let's stream the AI output to deepgram for faster synthesis