rename privacy "private" → "unlisted"; enable GPS for unlisted

- "unlisted" = not shown in the public feed, but GPS track, timeseries
  and detail JSON are all accessible by direct URL (security by obscurity)
- "private" accepted as legacy alias everywhere (backward compat with
  existing data on disk)
- New writes from Strava sync / ZIP upload / sidecar use "unlisted"
- Only "no_gps" now suppresses the GPS track
- isUnlisted() helper in format.ts used by all Svelte/Astro components
- SCHEMA.md and CLAUDE.md document the privacy model and the distinction
  between "unlisted" and "no_gps"

site/src/components/CommunityView.svelte

@@ -1,7 +1,7 @@
 <script lang="ts">
   import { onMount } from 'svelte';
   import type { BASIndex, ActivitySummary } from '../lib/types';
-  import { formatDistance, formatDuration, sportIcon } from '../lib/format';
+  import { formatDistance, formatDuration, isUnlisted, sportIcon } from '../lib/format';
 
   export let base: string = '/';
 
@@ -74,7 +74,7 @@
     const tot: Totals = { count: 0, distance_m: 0, elevation_m: 0, duration_s: 0, users: 0 };
 
     for (const u of rawUsers) {
-      const pub = u.activities.filter(a => a.privacy !== 'private');
+      const pub = u.activities.filter(a => !isUnlisted(a.privacy));
       const filtered = pub.filter(a => new Date(a.started_at) >= start);
 
       const stat: UserStat = {