feat(app): memory screen - browse the agent note graph on mobile

A new Memory tab loads /memory/graph when opened and lists the
distilled notes newest-first with kind filter chips
(fact/decision/gotcha/runbook); tapping a note expands its body, tags,
and both directions of its links, resolved to note titles. Read-only by
design — authoring stays with the web dashboard's admin surface and the
agents' own MCP server.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01731mKtVzsfeT4Vi3TvkR48

app/src/components/TabBar.tsx

@@ -15,6 +15,7 @@ import { useAppState, type Screen } from "../state/AppState";
 const TABS: { key: Screen; label: string; icon: IconName }[] = [
   { key: "fleet", label: "Fleet", icon: "home" },
   { key: "schedules", label: "Schedules", icon: "clock" },
+  { key: "memory", label: "Memory", icon: "brain" },
   { key: "log", label: "Log", icon: "file" },
   { key: "settings", label: "Settings", icon: "settings" },
 ];