feat(#52): era templates + shared scenario types/transforms

- presets/templates/: 3 light era templates (ww2/present/near-future) + index.json
  manifest (id, name, year, eraDescription, suggestedPowers, tensions).
- server/templates.ts: createTemplateStore (mirror of createPresetStore).
- shared/scenario.ts: dependency-free contract for the dynamic scenario path —
  SuggestedPower / EraTemplate / TemplateMeta / WorldNation / ScenarioEvent /
  WorldDraft / Checkpoint types, relationFromScore, validateWorldDraft (pure,
  defensive, never throws), worldDraftToGameState (region-key territory via the
  injected expand resolver, regionStats seeded, clean turn-1 state).
- tests: server/templates.test.ts (manifest order + file shape),
  server/scenario-shared.test.ts (15 cases: validation/clamp/dedup/null +
  transform).

Fixes #52

presets/templates/index.json

@@ -0,0 +1,20 @@
+[
+  {
+    "id": "ww2",
+    "name": "World War II",
+    "year": 1939,
+    "eraDescription": "Europe teeters on the brink of total war. Fascist powers press their advantage across the continent while the democracies marshal their strength."
+  },
+  {
+    "id": "present",
+    "name": "Present Day",
+    "year": 2026,
+    "eraDescription": "A multipolar world of blocs, sanctions, and tech supremacy. Climate strain, AI, and great-power rivalry shape every decision."
+  },
+  {
+    "id": "near-future",
+    "name": "Near Future",
+    "year": 2035,
+    "eraDescription": "Autonomous fleets, orbital assets, and climate-hamstrung coastlines. Old alliances strain under new technologies and old grievances."
+  }
+]

presets/templates/near-future.json

@@ -0,0 +1,17 @@
+{
+  "id": "near-future",
+  "name": "Near Future",
+  "year": 2035,
+  "eraDescription": "A near-future world: autonomous fleets, orbital assets, and climate-hamstrung coastlines. Old alliances strain under new technologies and old grievances as the great powers reach for the next horizon.",
+  "suggestedPowers": [
+    { "name": "North American Union", "region": "USA", "note": "The industrial-technological core of the West." },
+    { "name": "Chinese Federation", "region": "CHN", "note": "The integrated superpower of the Pacific." },
+    { "name": "European Confederation", "region": "FRA", "note": "The united European bloc." },
+    { "name": "Russian Union", "region": "RUS", "note": "The resource frontier state." }
+  ],
+  "tensions": [
+    "Autonomous weapons and the new arms race",
+    "Climate migration and resource wars",
+    "The contest for space and orbital dominance"
+  ]
+}

presets/templates/present.json

@@ -0,0 +1,17 @@
+{
+  "id": "present",
+  "name": "Present Day",
+  "year": 2026,
+  "eraDescription": "A multipolar world of blocs, sanctions, and tech supremacy. Climate strain, artificial intelligence, and great-power rivalry shape every decision the leaders of the age must make.",
+  "suggestedPowers": [
+    { "name": "United States", "region": "USA", "note": "The military-technological leader of the Western bloc." },
+    { "name": "People's Republic of China", "region": "CHN", "note": "The industrial giant pressing on the Western Pacific." },
+    { "name": "Russian Federation", "region": "RUS", "note": "A resource-rich power testing its neighbors' resolve." },
+    { "name": "European Union", "region": "FRA", "note": "A large, internally divided economic bloc." }
+  ],
+  "tensions": [
+    "US–China tech and trade rivalry",
+    "The war in Europe and the eastern flank",
+    "AI and cyber dominance"
+  ]
+}

presets/templates/ww2.json

@@ -0,0 +1,17 @@
+{
+  "id": "ww2",
+  "name": "World War II",
+  "year": 1939,
+  "eraDescription": "Europe teeters on the brink of total war. Fascist powers press their advantage across the continent while the democracies marshal their strength, and the great powers watch — and arm — from across the oceans.",
+  "suggestedPowers": [
+    { "name": "German Reich", "region": "DEU", "note": "A militarized Reich at the heart of the continent, its army the most battle-hardened in Europe." },
+    { "name": "United Kingdom", "region": "GBR", "note": "An island power that commands the seas but is cut off from the continent." },
+    { "name": "Soviet Union", "region": "RUS", "note": "A vast, fragile industrial giant on the eastern frontier." },
+    { "name": "United States", "region": "USA", "note": "An industrial colossus, still politically divided over entry into the war." }
+  ],
+  "tensions": [
+    "The Axis versus the Allies",
+    "The race for continental resources and sea lanes",
+    "The uneasy balance before the bomb"
+  ]
+}