Security audit and hardening

## Description
Conduct comprehensive security audit and implement security hardening measures.

## Security Areas to Audit
- [ ] Authentication and authorization
- [ ] Input validation and sanitization
- [ ] Database security and SQL injection prevention
- [ ] API security and rate limiting
- [ ] Agent communication security
- [ ] Data encryption and storage
- [ ] Network security and CORS

## Hardening Tasks
- [ ] Generate strong secrets and keys
- [ ] Implement security headers
- [ ] Add input validation middleware
- [ ] Configure secure CORS policies
- [ ] Implement audit logging
- [ ] Add security monitoring

## Priority: Critical
**Type**: Security
**Component**: All
**Estimated Effort**: 1-2 weeks

No files, tests, or entry points are named, so first map the Go project and identify where authentication, input handling, database access, APIs, agent communication, and network configuration are implemented. Done means the listed audit areas and hardening tasks have been addressed and their results are verified.

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