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

Makefile

@@ -5,7 +5,7 @@ SERVER_DIR := apps/server
 WEB_DIR := apps/web
 SERVER_BIN := $(SERVER_DIR)/bin/md-hub-secure
 
-.PHONY: web-install web-build server-run server-build server-test docker-build ci fmt
+.PHONY: web-install web-build web-dev server-run server-build server-test docker-build ci fmt dev dev-web dev-server
 
 web-install:
 	cd $(WEB_DIR) && $(NPM) install
@@ -13,6 +13,9 @@ web-install:
 web-build:
 	cd $(WEB_DIR) && $(NPM) run build
 
+web-dev:
+	cd $(WEB_DIR) && $(NPM) run dev
+
 server-run:
 	cd $(SERVER_DIR) && CGO_ENABLED=1 $(GO) run ./cmd/md-hub-secure
 
@@ -23,6 +26,24 @@ server-build:
 server-test:
 	cd $(SERVER_DIR) && CGO_ENABLED=1 $(GO) test ./...
 
+dev-server:
+	cd $(SERVER_DIR) && MD_HUB_DEV_VITE_URL=http://localhost:5173 air
+
+dev-web:
+	cd $(WEB_DIR) && $(NPM) run dev
+
+dev:
+	@echo "Starting dev servers..."
+	@echo "  - Go server (with air live reload) on http://localhost:8080"
+	@echo "  - Vite dev server on http://localhost:5173"
+	@echo ""
+	@echo "Access the app at http://localhost:8080/app/"
+	@echo ""
+	@trap 'kill %1 %2 2>/dev/null || true' EXIT; \
+	make dev-server & \
+	make dev-web & \
+	wait
+
 docker-build:
 	docker build -t md-hub-secure:dev .