Add 500km link cap, block-height-based claim expiry, and link count in score

- MAX_LINK_DISTANCE_KM (default 500): flat cap on link length. Real
  Ingress scales this off portal/resonator level (up to ~655km); Regress
  has no leveling system to scale off of, so this is a single ceiling.
- PORTAL_TIMEOUT_BLOCKS (default 2100): claims stamp the current Bitcoin
  block height (claimed_at_block, new migration) and expire back to
  neutral after this many blocks — the game's clock is block height, not
  wall-clock. Current height comes from mempool.space (BlockHeightService,
  60s cache), same trust model as the BTC Map dependency. A background
  sweep actively reverts timed-out claims (tearing down their links, same
  as a normal recapture); claim/link routes also check inline so
  correctness doesn't depend on sweep timing between runs.
- Pre-existing claims (already live in production) get backfilled with
  the real current block height once at startup rather than a guessed
  historical value — dry-run verified against an actual copy of the live
  production database before deploying.
- Score now reports link count per team alongside places/fields/area
  (backend already computed this; only the frontend display was missing).

22 new tests (53 total): pure expiry-logic unit tests plus full
claim/link/sweep integration tests using a network-free fake block-height
provider (BlockHeightProvider interface + FakeBlockHeight test double).

server/src/app.ts

@@ -6,6 +6,7 @@ import { existsSync } from 'node:fs';
 import { join } from 'node:path';
 import type { Config } from './config.js';
 import { openDatabase, type DB } from './db/database.js';
+import { BlockHeightService, type BlockHeightProvider } from './services/blockHeight.js';
 import nostrAuth from './plugins/nostr-auth.js';
 import authRoutes from './routes/auth.js';
 import placesRoutes from './routes/places.js';
@@ -17,6 +18,7 @@ import syncRoutes from './routes/sync.js';
 export interface AppContext {
   config: Config;
   db: DB;
+  blockHeight: BlockHeightProvider;
 }
 
 declare module 'fastify' {
@@ -29,6 +31,7 @@ export interface BuildAppOptions {
   config: Config;
   dbPath?: string; // override for tests (':memory:')
   logger?: boolean;
+  blockHeight?: BlockHeightProvider; // override for tests — avoids real network calls
 }
 
 export async function buildApp(opts: BuildAppOptions): Promise<FastifyInstance> {
@@ -37,7 +40,11 @@ export async function buildApp(opts: BuildAppOptions): Promise<FastifyInstance>
 
   const app = Fastify({ logger: opts.logger ?? true, bodyLimit: 1 * 1024 * 1024 });
 
-  const ctx: AppContext = { config, db };
+  const ctx: AppContext = {
+    config,
+    db,
+    blockHeight: opts.blockHeight ?? new BlockHeightService(config.BLOCK_HEIGHT_API_URL),
+  };
   app.decorate('ctx', ctx);
 
   await app.register(cookie);