Remove dead signup router, unused verification functions, and legacy cleanup query

- Delete src/routes/signup.ts (dead code, 410 handler in index.ts remains)
- Remove isEmailVerified() and getVerifiedApiKey() from verification.ts (only used by signup)
- Remove stale-key cleanup from cleanupStaleData() that queried legacy verifications table
- Update usage middleware message: 'Free tier limit' → 'Account limit'
- TDD: 8 new tests, removed signup.test.ts (dead), net 556 tests passing

src/__tests__/dead-signup-removal.test.ts

@@ -0,0 +1,44 @@
+import { describe, it, expect } from "vitest";
+import { readFileSync, existsSync } from "fs";
+import { join } from "path";
+
+describe("Dead Signup Router Removal", () => {
+  describe("Signup router module removed", () => {
+    it("should not have src/routes/signup.ts file", () => {
+      const signupPath = join(__dirname, "../routes/signup.ts");
+      expect(existsSync(signupPath)).toBe(false);
+    });
+  });
+
+  describe("Dead verification functions removed from source", () => {
+    it("should not export isEmailVerified from verification.ts source", () => {
+      const src = readFileSync(join(__dirname, "../services/verification.ts"), "utf8");
+      expect(src).not.toContain("export async function isEmailVerified");
+    });
+
+    it("should not export getVerifiedApiKey from verification.ts source", () => {
+      const src = readFileSync(join(__dirname, "../services/verification.ts"), "utf8");
+      expect(src).not.toContain("export async function getVerifiedApiKey");
+    });
+
+    it("should still export createPendingVerification", () => {
+      const src = readFileSync(join(__dirname, "../services/verification.ts"), "utf8");
+      expect(src).toContain("export async function createPendingVerification");
+    });
+
+    it("should still export verifyCode", () => {
+      const src = readFileSync(join(__dirname, "../services/verification.ts"), "utf8");
+      expect(src).toContain("export async function verifyCode");
+    });
+  });
+
+  describe("410 signup handler still works", () => {
+    it("should still have signup 410 handler working", async () => {
+      const request = (await import("supertest")).default;
+      const { app } = await import("../index.js");
+      const res = await request(app).post("/v1/signup/free");
+      expect(res.status).toBe(410);
+      expect(res.body.error).toContain("discontinued");
+    });
+  });
+});