Add search functionality (Issue #3)

Backend changes:
- Added search query parameter (q) to /api/posts endpoint
- Search filters posts by title, content, author, and source
- Case-insensitive search with substring matching

Frontend changes:
- Made search bar functional with Enter key and click support
- Added performSearch() function to trigger searches
- Added Clear Search button that appears during active search
- Search results update feed title to show query
- Integrated search with existing pagination and filtering
- Preserves anonymous/authenticated feed title when clearing search

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

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

templates/dashboard.html

@@ -447,6 +447,24 @@
     transform: translateY(-1px);
 }
 
+.clear-search-btn {
+    background: #f1f5f9;
+    color: #64748b;
+    border: 1px solid #e2e8f0;
+    padding: 10px 20px;
+    border-radius: 8px;
+    cursor: pointer;
+    font-size: 14px;
+    font-weight: 500;
+    transition: all 0.2s ease;
+}
+
+.clear-search-btn:hover {
+    background: #e2e8f0;
+    color: #2c3e50;
+    transform: translateY(-1px);
+}
+
 .feed-container {
     padding: 0;
 }
@@ -803,6 +821,7 @@ async function loadPosts(page = 1, community = '', platform = '', append = false
         params.append('per_page', 20);
         if (community) params.append('community', community);
         if (platform) params.append('platform', platform);
+        if (currentSearchQuery) params.append('q', currentSearchQuery);
 
         const response = await fetch(`/api/posts?${params}`);
         const data = await response.json();
@@ -1037,15 +1056,52 @@ function refreshFeed() {
 }
 
 // Search functionality
+let currentSearchQuery = '';
+
 document.querySelector('.search-input').addEventListener('keypress', function(e) {
     if (e.key === 'Enter') {
         const query = this.value.trim();
-        if (query) {
-            alert(`Search functionality coming soon! You searched for: "${query}"`);
-        }
+        performSearch(query);
     }
 });
 
+document.querySelector('.search-btn').addEventListener('click', function() {
+    const query = document.querySelector('.search-input').value.trim();
+    performSearch(query);
+});
+
+function performSearch(query) {
+    currentSearchQuery = query;
+    currentPage = 1;
+
+    if (query) {
+        document.querySelector('.content-header h1').textContent = `Search results for "${query}"`;
+        // Show clear search button
+        if (!document.querySelector('.clear-search-btn')) {
+            const clearBtn = document.createElement('button');
+            clearBtn.className = 'clear-search-btn';
+            clearBtn.textContent = '✕ Clear search';
+            clearBtn.onclick = clearSearch;
+            document.querySelector('.content-actions').prepend(clearBtn);
+        }
+    }
+
+    loadPosts();
+}
+
+function clearSearch() {
+    currentSearchQuery = '';
+    document.querySelector('.search-input').value = '';
+    // Restore original feed title based on user state
+    const isAnonymous = {{ 'true' if anonymous else 'false' }};
+    document.querySelector('.content-header h1').textContent = isAnonymous ? 'Public Feed' : 'Your Feed';
+    const clearBtn = document.querySelector('.clear-search-btn');
+    if (clearBtn) {
+        clearBtn.remove();
+    }
+    loadPosts();
+}
+
 // Setup infinite scroll functionality
 function setupInfiniteScroll() {
     if (!userSettings?.experience?.infinite_scroll) {