Addresses the root cause of issue #631 (infinite Docker agent restart loop)
and prevents similar issues with host-agent and sensor-proxy.
Changes:
- Set dockeragent.Version default to "dev" instead of hardcoded version
- Add version embedding to server build in Dockerfile
- Add version embedding to host-agent builds (all platforms)
- Add version embedding to sensor-proxy builds (all platforms)
This ensures:
1. Server's /api/agent/version endpoint returns correct v4.26.0
2. Downloaded agent binaries have matching embedded versions
3. Dev builds skip auto-update (Version="dev")
4. No version mismatch triggers infinite restart loops
Related to #631
