Logging cleanup

[dantheuber]

Summary

Replaces all console.log/warn/error calls across the server codebase with the structured pino logger, fixes all ESLint errors, and silences log output during tests — eliminating noisy, non-meaningful output from test runs.

Changes

Lint fixes

• Fixed 3 prefer-const errors in alertMutes.ts and mutes/list.ts by restructuring let assignments to inline const

Logging migration (console → pino logger)

• 15 route handlers migrated from manual console.error + res.status().json() to the centralized sendErrorResponse utility
• Auth routes (login.ts, logout.ts, callback.ts) now use logger.error/warn/info instead of console.*
• HealthPollingService.ts: all 8 console.log calls replaced with structured logger.info
• auth/config.ts, auth/session.ts, auth/validateSessionSecret.ts: console.log/warn → logger.info/warn
• db/index.ts, db/migrate.ts: console.log → logger.info

Error handling improvements

• errors.ts: errorHandler, wrapHandler, and sendErrorResponse now only log 5xx errors via logger.error — expected 4xx errors (validation, not-found) no longer produce log output
• Eliminates the main source of noisy test output: route handler tests triggering expected validation errors

Test output silencing

• Added LOG_LEVEL=silent to server/jest.config.js to suppress all pino output during tests
• Updated test files (errors.test.ts, config.test.ts, warnInsecureCookies.test.ts, validateSessionSecret.test.ts, HealthPollingService.test.ts) to mock the logger module instead of spying on console.*

Testing

• New/updated tests included
• All tests pass (npm test)
• Linting passes (npm run lint)

Checklist

• I have read the Contributing Guidelines
• I agree to the Contributor License Agreement
• My changes do not introduce security vulnerabilities
• Documentation updated (if applicable)