feat(website): add comprehensive accessibility improvements

Phase 1 - Screen Reader Critical:
- Add aria-label to main navigation
- Add accessible names to icon-only buttons (GitHub, theme toggle, close)
- Add aria-hidden to decorative SVGs and emoji icons
- Add role=dialog, aria-modal, aria-labelledby to modal
- Add skip link with visible focus state

Phase 2 - Keyboard Navigation:
- Implement focus trap in modal (Tab/Shift+Tab cycles)
- Return focus to trigger element on modal close
- Replace outline:none with visible focus rings
- Add keyboard navigation to install dropdown (arrows, escape)
- Add aria-expanded to dropdown toggles

Phase 3 - Dynamic Content:
- Add aria-live=polite to results counts and loading states
- Add role=listbox to search results
- Add role=list to resource lists
- Add role=menu/menuitem to dropdown menus

Phase 4 - Forms & Labels:
- Add .sr-only utility class for screen reader text
- Add visually hidden labels to all search inputs
- Add aria-label to filter dropdowns

Files modified:
- BaseLayout.astro, Modal.astro (ARIA attributes)
- modal.ts (focus trap, keyboard navigation)
- global.css (sr-only, skip-link, focus styles)
- All page files (labels, live regions, roles)

website/src/pages/tools.astro

@@ -7,7 +7,7 @@ import BaseLayout from "../layouts/BaseLayout.astro";
   description="MCP servers and developer tools for GitHub Copilot"
   activeNav="tools"
 >
-  <main>
+  <main id="main-content">
     <div class="page-header">
       <div class="container">
         <h1>🔧 Tools</h1>
@@ -19,6 +19,7 @@ import BaseLayout from "../layouts/BaseLayout.astro";
       <div class="container">
         <div class="search-section">
           <div class="search-bar">
+            <label for="search-input" class="sr-only">Search tools</label>
             <input
               type="text"
               id="search-input"
@@ -27,17 +28,18 @@ import BaseLayout from "../layouts/BaseLayout.astro";
             />
           </div>
           <div class="filters">
-            <select id="filter-category" class="filter-select">
+            <label for="filter-category" class="sr-only">Filter by category</label>
+            <select id="filter-category" class="filter-select" aria-label="Filter by category">
               <option value="">All Categories</option>
             </select>
             <button id="clear-filters" class="btn btn-secondary btn-small"
               >Clear</button
             >
           </div>
-          <div id="results-count" class="results-count"></div>
+          <div id="results-count" class="results-count" aria-live="polite"></div>
         </div>
 
-        <div id="tools-list"></div>
+        <div id="tools-list" role="list"></div>
 
         <div class="coming-soon">
           <h2>More Tools Coming Soon</h2>