Explore: personal GPS heatmap tab under Athlete page

- bincio/explore.py: bake_tracks() simplifies GPS coords (RDP ε=0.0001),
  strips to [lng,lat], groups by sport type, writes per-handle tracks.json
- bake-tracks CLI command; render CLI calls _bake_tracks() after each build;
  strava_zip runs it once at end of batch
- /api/me/tracks endpoint serves the baked file; wipe_user cleans it up
- Explore.svelte: MapLibre full-screen map with sidebar — type pills,
  year/month date filter, Lines / Heatmap (global or by-type) view modes
- AthleteView: Explore tab visible only to profile owner (checks __bincioMe)
- Base.astro: fullscreen prop + Planner nav link

site/src/pages/u/[handle]/athlete/explore/index.astro

@@ -0,0 +1,18 @@
+---
+import Base from '../../../../../layouts/Base.astro';
+import Explore from '../../../../../components/Explore.svelte';
+import { readShardHandles } from '../../../../../lib/manifest';
+
+export function getStaticPaths() {
+  return readShardHandles().map(({ handle }) => ({
+    params: { handle },
+    props: { handle },
+  }));
+}
+
+const { handle } = Astro.props as { handle: string };
+const base = import.meta.env.BASE_URL;
+---
+<Base title={`@${handle} Explore — BincioActivity`} fullscreen>
+  <Explore {handle} {base} client:only="svelte" />
+</Base>