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/database/migrations/000007_fts5.down.sql

@@ -0,0 +1 @@
+DROP TABLE IF EXISTS document_search;

apps/server/internal/database/migrations/000007_fts5.up.sql

@@ -0,0 +1,29 @@
+CREATE VIRTUAL TABLE IF NOT EXISTS document_search USING fts5(
+  title,
+  content,
+  path UNINDEXED,
+  tokenize='porter'
+);
+
+INSERT INTO document_search (rowid, title, content, path)
+SELECT rowid, title, '', path FROM documents;
+
+CREATE TRIGGER IF NOT EXISTS document_search_insert
+AFTER INSERT ON documents
+BEGIN
+  INSERT INTO document_search (rowid, title, content, path)
+  VALUES (NEW.rowid, NEW.title, '', NEW.path);
+END;
+
+CREATE TRIGGER IF NOT EXISTS document_search_update
+AFTER UPDATE ON documents
+BEGIN
+  UPDATE document_search SET title = NEW.title, path = NEW.path
+  WHERE rowid = NEW.rowid;
+END;
+
+CREATE TRIGGER IF NOT EXISTS document_search_delete
+AFTER DELETE ON documents
+BEGIN
+  DELETE FROM document_search WHERE rowid = OLD.rowid;
+END;