fix(labs): strict numeric parsing, atomic confirm guard, test integrity

- normalize.ts num(): parseFloat truncated at the first comma, so "1,200"
  silently became 1 (1000x error) and "5,5" became 5. Now strictly matches
  either US thousands-grouping or a plain number spanning the whole string;
  anything else (incl. ambiguous "5,5") returns null instead of a wrong value.
- labs.ts confirm handler: the pending-status check ran before the request
  body was read, so two concurrent confirms could both pass it and
  double-insert. Added a guarded UPDATE ... WHERE status = 'pending' as the
  first statement inside the existing synchronous transaction; zero rows
  affected throws and the route returns 409, with the fast-path check kept
  for the common case.
- Added missing `await` on two rejects.toThrow assertions (llm.test.ts,
  extract.test.ts) that were previously resolving before the assertion
  settled.
- Bumped the 11th-failed-login rate-limit test to a 30s timeout — 10
  sequential argon2id verifies can exceed bun:test's 5s default under load.

server/test/auth.test.ts

@@ -54,7 +54,7 @@ describe("auth", () => {
     // The global window applies to everyone, including a request with the correct password.
     const blocked = await app.request("/api/login", json({ password: "hunter2hunter2" }));
     expect(blocked.status).toBe(429);
-  });
+  }, 30000); // 10 sequential argon2id verifies can exceed the 5s default timeout
 
   test("unknown /api/* returns 404 when authed, 401 when unauthed", async () => {
     const app = makeApp();