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/.air.toml

@@ -0,0 +1,58 @@
+#:schema https://json.schemastore.org/any.json
+
+env_files = []
+root = "."
+testdata_dir = "testdata"
+tmp_dir = "tmp"
+
+[build]
+  args_bin = []
+  bin = "./bin/md-hub-secure"
+  cmd = "CGO_ENABLED=1 go build -trimpath -o bin/md-hub-secure ./cmd/md-hub-secure"
+  delay = 500
+  entrypoint = ["./bin/md-hub-secure"]
+  exclude_dir = ["assets", "tmp", "vendor", "testdata", "bin"]
+  exclude_file = []
+  exclude_regex = ["_test.go"]
+  exclude_unchanged = false
+  follow_symlink = false
+  full_bin = ""
+  ignore_dangerous_root_dir = false
+  include_dir = []
+  include_ext = ["go", "tpl", "tmpl", "html", "css", "js"]
+  include_file = []
+  kill_delay = "0s"
+  log = "build-errors.log"
+  poll = false
+  poll_interval = 0
+  post_cmd = []
+  pre_cmd = []
+  rerun = false
+  rerun_delay = 500
+  send_interrupt = true
+  stop_on_error = false
+
+[color]
+  app = ""
+  build = "yellow"
+  main = "magenta"
+  runner = "green"
+  watcher = "cyan"
+
+[log]
+  main_only = false
+  silent = false
+  time = false
+
+[misc]
+  clean_on_exit = false
+
+[proxy]
+  app_port = 0
+  app_start_timeout = 0
+  enabled = false
+  proxy_port = 0
+
+[screen]
+  clear_on_rebuild = false
+  keep_scroll = true