feat: add military bases map layer for Western Pacific

Add 18 US military bases (Japan, Guam, South Korea, Hawaii, Diego Garcia)
as a toggleable map layer. Follows the existing data center layer pattern:
static JSON → backend fetcher → slow-tier API → frontend GeoJSON layer.

Includes red circle markers with labels, click popups showing operator
and branch info, and a toggle in the left panel.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/tests/test_military_bases.py

@@ -0,0 +1,62 @@
+"""Tests for military bases data and fetcher."""
+import json
+from pathlib import Path
+from unittest.mock import patch
+
+import pytest
+
+from services.fetchers._store import latest_data, _data_lock
+
+
+BASES_PATH = Path(__file__).parent.parent / "data" / "military_bases.json"
+
+
+class TestMilitaryBasesData:
+    """Validate the static military_bases.json file."""
+
+    def test_json_file_exists(self):
+        assert BASES_PATH.exists()
+
+    def test_all_entries_have_required_fields(self):
+        raw = json.loads(BASES_PATH.read_text(encoding="utf-8"))
+        assert len(raw) > 0
+        for entry in raw:
+            assert "name" in entry and entry["name"]
+            assert "country" in entry and entry["country"]
+            assert "operator" in entry and entry["operator"]
+            assert "branch" in entry and entry["branch"]
+            assert "lat" in entry and isinstance(entry["lat"], (int, float))
+            assert "lng" in entry and isinstance(entry["lng"], (int, float))
+
+    def test_coordinates_in_valid_range(self):
+        raw = json.loads(BASES_PATH.read_text(encoding="utf-8"))
+        for entry in raw:
+            assert -90 <= entry["lat"] <= 90, f"{entry['name']} has invalid lat"
+            assert -180 <= entry["lng"] <= 180, f"{entry['name']} has invalid lng"
+
+    def test_branch_values_are_known(self):
+        known_branches = {"air_force", "navy", "marines", "army"}
+        raw = json.loads(BASES_PATH.read_text(encoding="utf-8"))
+        for entry in raw:
+            assert entry["branch"] in known_branches, f"{entry['name']} has unknown branch: {entry['branch']}"
+
+
+class TestFetchMilitaryBases:
+    """Test the fetcher populates latest_data correctly."""
+
+    def test_fetch_populates_store(self):
+        from services.fetchers.infrastructure import fetch_military_bases
+        fetch_military_bases()
+        with _data_lock:
+            bases = latest_data["military_bases"]
+        assert len(bases) > 0
+        assert all("name" in b and "lat" in b and "lng" in b for b in bases)
+
+    def test_includes_key_bases(self):
+        from services.fetchers.infrastructure import fetch_military_bases
+        fetch_military_bases()
+        with _data_lock:
+            names = {b["name"] for b in latest_data["military_bases"]}
+        assert "Kadena Air Base" in names
+        assert "Fleet Activities Yokosuka" in names
+        assert "Andersen Air Force Base" in names