Replace per-kind reclassify with a single global reclassify that respects manual and Race locks

Manual assignments are the user's definitive word and Race assignments come
from a hard Garmin fact (eventType.typeKey), not a retunable rule -- neither
is ever touched by reclassify again, and Race can no longer be set by hand
via the review queue. Adds an Activities page so this locked/unlocked status
is visible per workout, since Review Queue only ever showed unresolved items.

frontend/src/App.tsx

@@ -1,6 +1,7 @@
 import { useState } from "react";
 import "./App.css";
 import { GarminConnection } from "./components/GarminConnection";
+import { Activities } from "./pages/Activities";
 import { Dashboard } from "./pages/Dashboard";
 import { Profile } from "./pages/Profile";
 import { ReviewQueue } from "./pages/ReviewQueue";
@@ -9,6 +10,7 @@ import { WorkoutKinds } from "./pages/WorkoutKinds";
 const TABS = [
   { key: "dashboard", label: "Progression", Component: Dashboard },
   { key: "review", label: "Review Queue", Component: ReviewQueue },
+  { key: "activities", label: "Activities", Component: Activities },
   { key: "kinds", label: "Workout Kinds", Component: WorkoutKinds },
   { key: "profile", label: "Profile", Component: Profile },
 ] as const;