fix: make scheduler lock port configurable with automatic fallback

[Kailigithub]

Summary

On Windows, the scheduler's hardcoded lock port 45762 can conflict with the system's dynamic port range, causing WinError 10013 and preventing startup.

Changes

• Made the lock port configurable via SCHEDULER_LOCK_PORT environment variable (default: 45762)
• Added automatic port fallback: if the configured port is occupied, tries up to 10 consecutive ports
• Raises a clear RuntimeError if no port in the range can be bound

Root Cause

reflect/scheduler.py hardcoded 45762 for the lock socket. On Windows, if the dynamic port range (configurable via netsh) overlaps with this port, the bind() call fails with WinError 10013.

Testing

• All 3 existing tests pass (no regression)
• Verified: default port binding works correctly
• Verified: SCHEDULER_LOCK_PORT environment variable override works
• Verified: automatic fallback to next available port when the target port is occupied

Closes #331