feat: miller column browser, offline cache, search, breadcrumbs

- Dynamic miller column sizing with flexbox layout
- Root column (160px), middle slices (48px), active column (flex)
- Auto-scroll browser to rightmost column on navigation
- Offline indicator UI and IndexedDB cache integration
- /api/documents endpoint for client-side document caching
- Breadcrumb navigation in document content area
- FTS5 search with SQLite virtual table
- Client-side Mermaid and KaTeX rendering via CDN
- Deep sample content (advanced-topics/raft-deep-dive)
- Border removal (only search button keeps radius)
- Full viewport layout with proper borders between sidebar/content

apps/server/internal/httpserver/static/cache.js

@@ -0,0 +1,100 @@
+(function () {
+  const DB_NAME = "md-hub-cache";
+  const DB_VERSION = 1;
+  const STORE_DOCUMENTS = "documents";
+  const STORE_CONTENT = "content";
+
+  function openDB() {
+    return new Promise(function (resolve, reject) {
+      const request = indexedDB.open(DB_NAME, DB_VERSION);
+      request.onerror = function () {
+        reject(request.error);
+      };
+      request.onsuccess = function () {
+        resolve(request.result);
+      };
+      request.onupgradeneeded = function (event) {
+        const db = event.target.result;
+        if (!db.objectStoreNames.contains(STORE_DOCUMENTS)) {
+          db.createObjectStore(STORE_DOCUMENTS, { keyPath: "path" });
+        }
+        if (!db.objectStoreNames.contains(STORE_CONTENT)) {
+          db.createObjectStore(STORE_CONTENT, { keyPath: "path" });
+        }
+      };
+    });
+  }
+
+  function cacheDocuments(documents) {
+    return openDB().then(function (db) {
+      return new Promise(function (resolve, reject) {
+        const tx = db.transaction(STORE_DOCUMENTS, "readwrite");
+        const store = tx.objectStore(STORE_DOCUMENTS);
+        documents.forEach(function (doc) {
+          store.put(doc);
+        });
+        tx.oncomplete = function () {
+          resolve();
+        };
+        tx.onerror = function () {
+          reject(tx.error);
+        };
+      });
+    });
+  }
+
+  function cacheContent(path, html, title) {
+    return openDB().then(function (db) {
+      return new Promise(function (resolve, reject) {
+        const tx = db.transaction(STORE_CONTENT, "readwrite");
+        const store = tx.objectStore(STORE_CONTENT);
+        store.put({ path: path, html: html, title: title, cachedAt: Date.now() });
+        tx.oncomplete = function () {
+          resolve();
+        };
+        tx.onerror = function () {
+          reject(tx.error);
+        };
+      });
+    });
+  }
+
+  function getCachedDocuments() {
+    return openDB().then(function (db) {
+      return new Promise(function (resolve, reject) {
+        const tx = db.transaction(STORE_DOCUMENTS, "readonly");
+        const store = tx.objectStore(STORE_DOCUMENTS);
+        const request = store.getAll();
+        request.onsuccess = function () {
+          resolve(request.result);
+        };
+        request.onerror = function () {
+          reject(request.error);
+        };
+      });
+    });
+  }
+
+  function getCachedContent(path) {
+    return openDB().then(function (db) {
+      return new Promise(function (resolve, reject) {
+        const tx = db.transaction(STORE_CONTENT, "readonly");
+        const store = tx.objectStore(STORE_CONTENT);
+        const request = store.get(path);
+        request.onsuccess = function () {
+          resolve(request.result);
+        };
+        request.onerror = function () {
+          reject(request.error);
+        };
+      });
+    });
+  }
+
+  window.MDHubCache = {
+    cacheDocuments: cacheDocuments,
+    cacheContent: cacheContent,
+    getCachedDocuments: getCachedDocuments,
+    getCachedContent: getCachedContent,
+  };
+})();