fix: contour overlay with pmtiles fork, absolute URL, extended zoom range

- Switch to @acalcutt/maplibre-contour-pmtiles for PMTiles support
- Use absolute URL for DemSource so Web Worker can resolve path
- Extend contour thresholds from z3-z15 for full zoom coverage
- Improve line styling with zoom-dependent width
- Improve label styling with bold font and better halo

Co-Authored-By: Claude <noreply@anthropic.com>

package-lock.json

@@ -8,11 +8,11 @@
       "name": "navi",
       "version": "0.0.0",
       "dependencies": {
+        "@acalcutt/maplibre-contour-pmtiles": "^0.1.2",
         "@dnd-kit/core": "^6.3.1",
         "@dnd-kit/sortable": "^10.0.0",
         "@dnd-kit/utilities": "^3.2.2",
         "lucide-react": "^1.8.0",
-        "maplibre-contour": "^0.1.0",
         "maplibre-gl": "^5.23.0",
         "opening_hours": "^3.12.0",
         "pmtiles": "^4.4.1",
@@ -38,6 +38,12 @@
         "vite": "^8.0.9"
       }
     },
+    "node_modules/@acalcutt/maplibre-contour-pmtiles": {
+      "version": "0.1.2",
+      "resolved": "https://registry.npmjs.org/@acalcutt/maplibre-contour-pmtiles/-/maplibre-contour-pmtiles-0.1.2.tgz",
+      "integrity": "sha512-dCyJFLLM4NomLoJ22McRp7yETFmzUuA6iEMVJS6+mFyHoNk7Sv6RI4Hn0DhGKeyjcJgan3YnfSnzsqRinnXSug==",
+      "license": "BSD-3-Clause"
+    },
     "node_modules/@alloc/quick-lru": {
       "version": "5.2.0",
       "resolved": "https://registry.npmjs.org/@alloc/quick-lru/-/quick-lru-5.2.0.tgz",
@@ -2686,12 +2692,6 @@
         "@jridgewell/sourcemap-codec": "^1.5.5"
       }
     },
-    "node_modules/maplibre-contour": {
-      "version": "0.1.0",
-      "resolved": "https://registry.npmjs.org/maplibre-contour/-/maplibre-contour-0.1.0.tgz",
-      "integrity": "sha512-H8muT7JWYE4oLbFv7L2RSbIM1NOu5JxjA9P/TQqhODDnRChE8ENoDkQIWOKgfcKNU77ypLk2ggGoh4/pt4UPLA==",
-      "license": "BSD-3-Clause"
-    },
     "node_modules/maplibre-gl": {
       "version": "5.23.0",
       "resolved": "https://registry.npmjs.org/maplibre-gl/-/maplibre-gl-5.23.0.tgz",