Add btop, overclock wizard option, click-to-copy decode UI

- setup.sh: Add btop to apt install for temp monitoring
- first-boot-wizard: Add Step 4 for overclock configuration
  - Detects Pi 4/5 model
  - Asks about active cooling
  - Offers appropriate overclock settings (2.0GHz Pi4, 2.8GHz Pi5)
  - Prompts for restart if enabled
- decode.html: Make message box click-to-copy, remove separate button
  - Shows "(click to copy)" hint
  - Visual feedback on hover and copy

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

rpi/setup.sh

@@ -148,7 +148,8 @@ sudo apt-get install -y \
     liblzma-dev \
     libzbar0 \
     libjpeg-dev \
-    python3-dev
+    python3-dev \
+    btop
 
 echo -e "${GREEN}[3/11]${NC} Installing gum (TUI toolkit)..."
 # Add Charm repo for gum