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/services/db.ts

@@ -172,8 +172,8 @@ export async function initDatabase(): Promise<void> {
  * - Unverified free-tier API keys (never completed verification)
  * - Orphaned usage rows (key no longer exists)
  */
-export async function cleanupStaleData(): Promise<{ expiredVerifications: number; staleKeys: number; orphanedUsage: number }> {
-  const results = { expiredVerifications: 0, staleKeys: 0, orphanedUsage: 0 };
+export async function cleanupStaleData(): Promise<{ expiredVerifications: number; orphanedUsage: number }> {
+  const results = { expiredVerifications: 0, orphanedUsage: 0 };
 
   // 1. Delete expired pending verifications
   const pv = await queryWithRetry(
@@ -181,18 +181,7 @@ export async function cleanupStaleData(): Promise<{ expiredVerifications: number
   );
   results.expiredVerifications = pv.rowCount || 0;
 
-  // 2. Delete unverified free-tier keys (email not in verified verifications)
-  const sk = await queryWithRetry(`
-    DELETE FROM api_keys
-    WHERE tier = 'free'
-      AND email NOT IN (
-        SELECT DISTINCT email FROM verifications WHERE verified_at IS NOT NULL
-      )
-    RETURNING key
-  `);
-  results.staleKeys = sk.rowCount || 0;
-
-  // 3. Delete orphaned usage rows
+  // 2. Delete orphaned usage rows (key no longer exists in api_keys)
   const ou = await queryWithRetry(`
     DELETE FROM usage
     WHERE key NOT IN (SELECT key FROM api_keys)
@@ -202,7 +191,7 @@ export async function cleanupStaleData(): Promise<{ expiredVerifications: number
 
   logger.info(
     { ...results },
-    `Database cleanup complete: ${results.expiredVerifications} expired verifications, ${results.staleKeys} stale keys, ${results.orphanedUsage} orphaned usage rows removed`
+    `Database cleanup complete: ${results.expiredVerifications} expired verifications, ${results.orphanedUsage} orphaned usage rows removed`
   );
 
   return results;