Block unmocked external requests in E2E tests

Surface net for the class of bug we hit in #282 — a POI test silently
relied on a live Overpass server for months because its `page.route`
mock was targeting a URL the browser no longer hit directly. CI stayed
green on coincidence (real OSM data happened to satisfy the "any
marker renders" assertion) until upstream behaviour drifted.

Add a shared Playwright fixture (e2e/fixtures/test.ts) that installs a
catch-all `page.route("**", ...)` before each test. Requests to
localhost + known tile CDNs pass through via `route.continue()`;
anything else is aborted and accumulated. At test teardown, a non-empty
blocked list throws, failing the test with the offending URLs and a
pointer to the fixture.

All seven e2e *.test.ts files updated to import test/expect (+ types)
from ./fixtures/test.

Full suite passes with this fixture in place (50/50 at --workers=2;
catch-all never fires, meaning no test currently relies on an
unallowlisted external service).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

e2e/demo-bot.test.ts

@@ -1,4 +1,4 @@
-import { test, expect } from "@playwright/test";
+import { test, expect } from "./fixtures/test";
 import postgres from "postgres";
 import { randomUUID } from "node:crypto";