feat: implement contextual help system with searchable overlay

- Add '?' button in status bar that opens help overlay
- Fuzzy search across 37 help articles covering major features
- Sample articles include: sensing links, detection quality, presence prediction, Fresnel zone
- Articles stored as static JSON (dashboard/help_articles.json)
- No server round-trip - all client-side
- Keyboard shortcut: Ctrl+? / Cmd+?

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

dashboard/index.html

@@ -3161,6 +3161,7 @@
     <!-- Guided Troubleshooting -->
     <script src="js/guided-help.js"></script>
     <script src="js/briefing.js"></script>
+    <script src="js/help.js"></script>
 
     <!-- Room editor panel -->
     <div id="room-editor-panel">

dashboard/js/help.js

@@ -121,8 +121,8 @@
      * Add help button to expert mode header
      */
     function addHelpButton() {
-        // Look for expert mode header
-        const header = document.querySelector('.expert-header, .view-header, .toolbar');
+        // Look for expert mode header or status bar
+        const header = document.querySelector('.expert-header, .view-header, .toolbar, #status-bar');
         if (!header) {
             // Try again after a delay
             setTimeout(addHelpButton, 1000);