UX polish: toned gold, cleaner labels, dropdown chevrons

- Toned down gold colors for better cross-monitor consistency
  - Header gold: #fee862 → #e5d058
  - Form labels: #ffe699 → #d9c580
- Removed text-shadow/outline from form labels (was smudgy)
- Removed background from nav floating labels
- More subtle nav hover background (halved opacity)
- Gold chevron on all dropdown selects for clarity
- Removed (environment) tag from channel key display
- Simplified channel key config text in about page
- Generate page: icon-only button for channel key

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

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

frontends/web/templates/generate.html

@@ -100,8 +100,8 @@
                                     <span class="input-group-text"><i class="bi bi-key"></i></span>
                                     <input type="text" class="form-control font-monospace" id="channelKeyGenerated"
                                            placeholder="Click Generate to create a key" readonly>
-                                    <button class="btn btn-outline-primary" type="button" id="generateChannelKeyBtn">
-                                        <i class="bi bi-shuffle me-1"></i>Generate
+                                    <button class="btn btn-outline-primary" type="button" id="generateChannelKeyBtn" title="Generate Channel Key">
+                                        <i class="bi bi-shuffle"></i>
                                     </button>
                                     <button class="btn btn-outline-secondary" type="button" id="copyChannelKeyBtn" disabled title="Copy to clipboard">
                                         <i class="bi bi-clipboard"></i>