feat(proxy-fitness): egress geo probe + unstable detection + state sweeper

Background probe fetches ipinfo through each pool itself (provider-agnostic
transport), fills an egress IP/country cache (TTL 1h, 8-IP history) and flags
flapping relays as unstable. Periodic state sweeper (10 min) prunes expired
fitness marks, stale geo/ip-history and Freebuff session/cooldown state;
schedulers skip non-server runtimes. Unit tests for the geo cache.

tests/unit/pool-geo.test.js

@@ -0,0 +1,26 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { setPoolGeo, getPoolGeo, poolGeoSnapshot, pruneStaleGeo, resetPoolGeo } from "open-sse/services/poolGeo.js";
+
+describe("pool egress geo cache", () => {
+  beforeEach(() => resetPoolGeo());
+
+  it("stores geo and classifies stability from egress changes", () => {
+    setPoolGeo("p1", { ip: "1.1.1.1", country: "US" });
+    setPoolGeo("p1", { ip: "1.1.1.1", country: "US" }); // same IP twice
+    expect(getPoolGeo("p1").isUnstable).toBe(false);
+    expect(getPoolGeo("p1").ipCount).toBe(1);
+
+    setPoolGeo("p1", { ip: "2.2.2.2", country: "US" }); // changed
+    expect(getPoolGeo("p1").isUnstable).toBe(true);
+    expect(getPoolGeo("p1").ipCount).toBe(2);
+  });
+
+  it("prunes TTL-stale entries (ipHistory rides along)", () => {
+    setPoolGeo("p1", { ip: "1.1.1.1", country: "US" });
+    setPoolGeo("p1", { ip: "2.2.2.2", country: "US" });
+    const cache = globalThis["__9routerPoolGeo__"];
+    cache.get("p1").ts = Date.now() - 2 * 60 * 60 * 1000;
+    expect(pruneStaleGeo()).toBe(1);
+    expect(poolGeoSnapshot()).toEqual({});
+  });
+});