feat(#50): make the four 0-100 stats consequential

- Add a hard military conquest gate (canConquer, CONQUEST_MILITARY_MARGIN=15)
  enforced in applyTurnResult: a contested invasion is repelled when the
  attacker's military is more than 15 below the defender's; re-claims of
  unowned regions are never gated. Emits a new 'repelled' event.
- Document the soft levers in the system prompt: stability<30 + gathering
  marker -> non-military takeover; economy growth/decay drives other stats.
- Emit bounded frontierMilitary (per-neighbour balance) and takeoverRisks
  hints in the user payload (only when present).
- repelled outcome color (#9f1239); full unit test coverage; stub untouched.
- Bump to v0.30.0.

Fixes #50

server/index.ts

@@ -314,6 +314,10 @@ app.post('/api/games/:id/jump', async (req, res) => {
       // pure (validKeys + regionName) and degrades to a key-only match when
       // the manifest is absent.
       regionKeyResolver: (ref) => resolveRegionKey(ref, validKeys(), (k) => regionName(k)),
+      // (v0.30, #50) region display name for the engine's "invasion repelled"
+      // event (geo properties.name, else the raw key). Always on — the
+      // resolver is pure and degrades to the key when the manifest is absent.
+      regionNameOf: (k) => regionName(k),
     });
     db.save(state);
     broadcast(id, 'turn', { state, result });