Go global: worldwide BTC Map sync, marker clustering, response compression

- Sync now pulls every BTC Map place worldwide (~29k live), not just
  Madeira — dropped BTCMAP_CENTER_LAT/LON/RADIUS_KM entirely.
- Incremental via a stored watermark (settings.btcmap_synced_since):
  only fetches what changed since the last sync, not the whole dataset
  every time. Handles deletions too (BTC Map delistings correctly evict
  the local place + cascade its claim/links, not just go unclaimed).
- Real bug caught and fixed before it shipped: tried BTC Map's own
  recommended updated_since+limit pagination first, but their timestamps
  mix millisecond and whole-second precision, and naive string comparison
  across that isn't chronologically safe — silently truncated a real
  sync to ~4,000 of ~42,000 records with no error. Measured the
  alternative (single unpaginated request) instead: 2-3s for the full
  dataset, simpler and actually correct. Full writeup in
  services/btcmap.ts, regression test for the specific bug in
  services/btcmap.test.ts.
- @fastify/compress added — the places list is now tens of thousands of
  rows, gzip/br/zstd auto-negotiated.
- Also fixed while touching dependencies: @fastify/static had a real
  high-severity path-traversal/auth-bypass advisory (GHSA-pr96-94w5-mx2h
  et al) affecting the version we were pinned to — bumped to the patched
  10.1.2.
- Frontend: leaflet.markercluster (raw per-marker rendering doesn't scale
  to tens of thousands of points), cyberpunk-themed cluster icons to
  match the existing HUD styling, batch marker insertion (addLayers, not
  a per-marker addLayer loop) since that's dramatically faster at this
  scale. Default map view is now world-scale, recentering on the
  player's location if geolocation is available.
- 60 backend tests passing throughout (7 new for the sync rewrite).

frontend/package-lock.json

@@ -9,12 +9,14 @@
       "version": "0.1.0",
       "dependencies": {
         "leaflet": "^1.9.4",
+        "leaflet.markercluster": "^1.5.3",
         "nostr-tools": "^2.24.1",
         "pinia": "^3.0.0",
         "vue": "^3.5.0"
       },
       "devDependencies": {
         "@types/leaflet": "^1.9.12",
+        "@types/leaflet.markercluster": "^1.5.6",
         "@vitejs/plugin-vue": "^6.0.0",
         "autoprefixer": "^10.4.20",
         "postcss": "^8.5.0",
@@ -1074,6 +1076,16 @@
         "@types/geojson": "*"
       }
     },
+    "node_modules/@types/leaflet.markercluster": {
+      "version": "1.5.6",
+      "resolved": "https://registry.npmjs.org/@types/leaflet.markercluster/-/leaflet.markercluster-1.5.6.tgz",
+      "integrity": "sha512-I7hZjO2+isVXGYWzKxBp8PsCzAYCJBc29qBdFpquOCkS7zFDqUsUvkEOyQHedsk/Cy5tocQzf+Ndorm5W9YKTQ==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@types/leaflet": "^1.9"
+      }
+    },
     "node_modules/@vitejs/plugin-vue": {
       "version": "6.0.8",
       "resolved": "https://registry.npmjs.org/@vitejs/plugin-vue/-/plugin-vue-6.0.8.tgz",
@@ -1862,6 +1874,15 @@
       "integrity": "sha512-nxS1ynzJOmOlHp+iL3FyWqK89GtNL8U8rvlMOsQdTTssxZwCXh8N2NB3GDQOL+YR3XnWyZAxwQixURb+FA74PA==",
       "license": "BSD-2-Clause"
     },
+    "node_modules/leaflet.markercluster": {
+      "version": "1.5.3",
+      "resolved": "https://registry.npmjs.org/leaflet.markercluster/-/leaflet.markercluster-1.5.3.tgz",
+      "integrity": "sha512-vPTw/Bndq7eQHjLBVlWpnGeLa3t+3zGiuM7fJwCkiMFq+nmRuG3RI3f7f4N4TDX7T4NpbAXpR2+NTRSEGfCSeA==",
+      "license": "MIT",
+      "peerDependencies": {
+        "leaflet": "^1.3.1"
+      }
+    },
     "node_modules/lilconfig": {
       "version": "3.1.3",
       "resolved": "https://registry.npmjs.org/lilconfig/-/lilconfig-3.1.3.tgz",