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>

frontends/web/templates/decode.html

@@ -120,13 +120,11 @@
                     <h6><i class="bi bi-check-circle me-2"></i>Message Decrypted Successfully!</h6>
                 </div>
                
-                <label class="form-label text-muted">Decoded Message:</label>
-                <div class="alert-message p-3 rounded bg-dark border border-secondary mb-2" id="decodedContent" style="white-space: pre-wrap;">{{ decoded_message }}</div>
-                <div class="d-flex justify-content-end mb-3">
-                    <button class="btn btn-sm btn-outline-light" onclick="navigator.clipboard.writeText(document.getElementById('decodedContent').innerText).then(() => { this.innerHTML = '<i class=\'bi bi-check\'></i> Copied!'; setTimeout(() => this.innerHTML = '<i class=\'bi bi-clipboard\'></i> Copy', 2000); }).catch(() => alert('Failed to copy'))">
-                        <i class="bi bi-clipboard"></i> Copy
-                    </button>
-                </div>
+                <label class="form-label text-muted">Decoded Message: <small class="text-secondary">(click to copy)</small></label>
+                <div class="alert-message p-3 rounded bg-dark border border-secondary mb-3" id="decodedContent" style="white-space: pre-wrap; cursor: pointer; transition: border-color 0.2s;"
+                     onclick="navigator.clipboard.writeText(this.innerText).then(() => { this.style.borderColor = '#198754'; this.dataset.origText = this.innerHTML; this.innerHTML = '<i class=\'bi bi-check-circle text-success\'></i> Copied to clipboard!'; setTimeout(() => { this.innerHTML = this.dataset.origText; this.style.borderColor = ''; }, 1500); }).catch(() => alert('Failed to copy'))"
+                     onmouseover="this.style.borderColor = '#6c757d'"
+                     onmouseout="this.style.borderColor = ''">{{ decoded_message }}</div>
 
                 <a href="/decode" class="btn btn-outline-light w-100">
                     <i class="bi bi-arrow-repeat me-2"></i>Decode Another