feat: add /search command to highlight matches in conversation

Closes #32

src/lib/components/Markdown.svelte

@@ -6,9 +6,10 @@
 
   interface Props {
     content: string;
+    searchQuery?: string;
   }
 
-  let { content }: Props = $props();
+  let { content, searchQuery = "" }: Props = $props();
   let containerElement: HTMLDivElement;
 
   const renderer = new marked.Renderer();
@@ -52,10 +53,47 @@
     return processed;
   }
 
+  function highlightSearchMatches(html: string, query: string): string {
+    if (!query) return html;
+
+    const codeBlockPlaceholders: string[] = [];
+    const tagPlaceholders: string[] = [];
+
+    // Temporarily replace code blocks with placeholders (don't highlight in code)
+    let processed = html.replace(/<(pre|code)[^>]*>[\s\S]*?<\/\1>/gi, (match) => {
+      codeBlockPlaceholders.push(match);
+      return `__CODE_SEARCH_PLACEHOLDER_${codeBlockPlaceholders.length - 1}__`;
+    });
+
+    // Temporarily replace all HTML tags with placeholders
+    processed = processed.replace(/<[^>]+>/g, (match) => {
+      tagPlaceholders.push(match);
+      return `__TAG_PLACEHOLDER_${tagPlaceholders.length - 1}__`;
+    });
+
+    // Apply search highlighting to text content
+    const escapedQuery = query.replace(/[.*+?^${}()|[\]\\]/g, "\\$&");
+    const regex = new RegExp(`(${escapedQuery})`, "gi");
+    processed = processed.replace(regex, '<mark class="search-highlight">$1</mark>');
+
+    // Restore HTML tags
+    processed = processed.replace(/__TAG_PLACEHOLDER_(\d+)__/g, (_, index) => {
+      return tagPlaceholders[parseInt(index)];
+    });
+
+    // Restore code blocks
+    processed = processed.replace(/__CODE_SEARCH_PLACEHOLDER_(\d+)__/g, (_, index) => {
+      return codeBlockPlaceholders[parseInt(index)];
+    });
+
+    return processed;
+  }
+
   function renderMarkdown(text: string): string {
     try {
       const html = marked.parse(text) as string;
-      return processSpoilers(html);
+      const withSpoilers = processSpoilers(html);
+      return highlightSearchMatches(withSpoilers, searchQuery);
     } catch {
       return text;
     }
@@ -304,4 +342,11 @@
     color: var(--text-primary);
     user-select: text;
   }
+
+  .markdown-content :global(.search-highlight) {
+    background-color: var(--search-highlight, #fbbf24);
+    color: var(--search-highlight-text, #000);
+    border-radius: 2px;
+    padding: 0 2px;
+  }
 </style>