feat: add smart map view with location-level clustering

- /map page with Leaflet (CartoDB dark tiles)
- Photos clustered by city/country (not per-photo)
- /api/map endpoint with encrypted cover asset IDs
- Configurable via gallery.yaml (map: true/false)
- Conditional nav link in header
- CSP updated for Leaflet CDN and tile servers
- Theme-aware popups with cover thumbnails and album links

package-lock.json

@@ -8,8 +8,10 @@
       "name": "immich-lightbox",
       "version": "0.1.0",
       "dependencies": {
+        "@types/leaflet": "^1.9.21",
         "gray-matter": "^4.0.3",
         "js-yaml": "^4.1.1",
+        "leaflet": "^1.9.4",
         "next": "16.1.6",
         "react": "19.2.3",
         "react-dom": "19.2.3",
@@ -2112,6 +2114,12 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@types/geojson": {
+      "version": "7946.0.16",
+      "resolved": "https://registry.npmjs.org/@types/geojson/-/geojson-7946.0.16.tgz",
+      "integrity": "sha512-6C8nqWur3j98U6+lXDfTUWIfgvZU+EumvpHKcYjujKH7woYyLj2sUmff0tRhrqM7BohUw7Pz3ZB1jj2gW9Fvmg==",
+      "license": "MIT"
+    },
     "node_modules/@types/js-yaml": {
       "version": "4.0.9",
       "resolved": "https://registry.npmjs.org/@types/js-yaml/-/js-yaml-4.0.9.tgz",
@@ -2133,6 +2141,15 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@types/leaflet": {
+      "version": "1.9.21",
+      "resolved": "https://registry.npmjs.org/@types/leaflet/-/leaflet-1.9.21.tgz",
+      "integrity": "sha512-TbAd9DaPGSnzp6QvtYngntMZgcRk+igFELwR2N99XZn7RXUdKgsXMR+28bUO0rPsWp8MIu/f47luLIQuSLYv/w==",
+      "license": "MIT",
+      "dependencies": {
+        "@types/geojson": "*"
+      }
+    },
     "node_modules/@types/node": {
       "version": "20.19.33",
       "resolved": "https://registry.npmjs.org/@types/node/-/node-20.19.33.tgz",
@@ -5512,6 +5529,12 @@
         "node": ">=0.10"
       }
     },
+    "node_modules/leaflet": {
+      "version": "1.9.4",
+      "resolved": "https://registry.npmjs.org/leaflet/-/leaflet-1.9.4.tgz",
+      "integrity": "sha512-nxS1ynzJOmOlHp+iL3FyWqK89GtNL8U8rvlMOsQdTTssxZwCXh8N2NB3GDQOL+YR3XnWyZAxwQixURb+FA74PA==",
+      "license": "BSD-2-Clause"
+    },
     "node_modules/levn": {
       "version": "0.4.1",
       "resolved": "https://registry.npmjs.org/levn/-/levn-0.4.1.tgz",