fix: improve test coverage accuracy and fix session timestamp bug

- Exclude seed files from coverage (not business logic)
- Fix Date.now() double call bug in createSession functions
- Coverage improved: 53.13% → 54.18%
- All 122 test suites passing

jest.config.js

@@ -8,6 +8,7 @@ module.exports = {
     '!src/**/*.d.ts',
     '!src/**/*.stories.{ts,tsx}',
     '!src/**/__tests__/**',
+    '!src/db/seed*.ts',
   ],
   coverageThreshold: {
     global: {