feat(website): Add last updated dates for agents, prompts, instructions, and skills

- Add git-dates.mjs utility to extract file modification dates from git history
- Include lastUpdated field in JSON data for all resource types
- Display relative time (e.g., '3 days ago') with full date on hover
- Add 'Recently Updated' sort option to agents, prompts, instructions, and skills pages
- Update deploy-website.yml to use fetch-depth: 0 for full git history

CI overhead: ~20-30s additional for full git checkout

website/src/pages/agents.astro

@@ -35,6 +35,13 @@ import Modal from '../components/Modal.astro';
               Has Handoffs
             </label>
           </div>
+          <div class="filter-group">
+            <label for="sort-select">Sort:</label>
+            <select id="sort-select" aria-label="Sort by">
+              <option value="title">Name (A-Z)</option>
+              <option value="lastUpdated">Recently Updated</option>
+            </select>
+          </div>
           <button id="clear-filters" class="btn btn-secondary btn-small">Clear Filters</button>
         </div>
         

website/src/pages/instructions.astro

@@ -24,6 +24,13 @@ import Modal from '../components/Modal.astro';
             <label for="filter-extension">File Extension:</label>
             <select id="filter-extension" multiple aria-label="Filter by file extension"></select>
           </div>
+          <div class="filter-group">
+            <label for="sort-select">Sort:</label>
+            <select id="sort-select" aria-label="Sort by">
+              <option value="title">Name (A-Z)</option>
+              <option value="lastUpdated">Recently Updated</option>
+            </select>
+          </div>
           <button id="clear-filters" class="btn btn-secondary btn-small">Clear Filters</button>
         </div>
         

website/src/pages/prompts.astro

@@ -24,6 +24,13 @@ import Modal from '../components/Modal.astro';
             <label for="filter-tool">Tool:</label>
             <select id="filter-tool" multiple aria-label="Filter by tool"></select>
           </div>
+          <div class="filter-group">
+            <label for="sort-select">Sort:</label>
+            <select id="sort-select" aria-label="Sort by">
+              <option value="title">Name (A-Z)</option>
+              <option value="lastUpdated">Recently Updated</option>
+            </select>
+          </div>
           <button id="clear-filters" class="btn btn-secondary btn-small">Clear Filters</button>
         </div>
         

website/src/pages/skills.astro

@@ -30,6 +30,13 @@ import Modal from '../components/Modal.astro';
               Has Bundled Assets
             </label>
           </div>
+          <div class="filter-group">
+            <label for="sort-select">Sort:</label>
+            <select id="sort-select" aria-label="Sort by">
+              <option value="title">Name (A-Z)</option>
+              <option value="lastUpdated">Recently Updated</option>
+            </select>
+          </div>
           <button id="clear-filters" class="btn btn-secondary btn-small">Clear Filters</button>
         </div>