feat: implement automatic host port selection for Docker environment

[vikashship]

Description

This PR introduces automatic host port selection for the Docker environment so local startup does not fail when default ports are already in use.

Instead of stopping with address already in use errors, the startup flow now checks configured host ports and automatically moves to the next available port.

Why This Change

Local development frequently fails when common ports like MongoDB, Redis, API, or Nginx ports are occupied by other services. This creates unnecessary setup friction and blocks contributors.

What This PR Adds

• Automatic port availability detection before Docker startup
• Incremental fallback logic to the next free host port
• Export of resolved port values for compose startup
• Startup logs that clearly show final selected ports
• Updated Docker startup commands to use the new resolver flow

Behavior Change

Before:

• Startup failed immediately when a configured port was busy

After:

• Startup continues by selecting the next free port automatically

Impact

• Better developer experience during setup and daily runs
• Fewer startup failures on shared/local machines
• Non-breaking change to application runtime behavior

Testing Done

• Verified resolver script syntax and execution path
• Verified Docker startup command integration
• Confirmed pre-commit workflow remains unaffected
• Confirmed resolved ports are printed for visibility

Notes

• Existing port environment variables are still supported
• Configured values now act as preferred starting ports, with automatic fallback when unavailable