Assign Dynamo system ports by launch role

[nv-roverman]

Summary

• Assign explicit Dynamo system ports to frontend processes.
• Reserve backend system-port ranges based on gpus_per_node.
• Derive MPI worker DYN_SYSTEM_PORT from the assigned base plus SLURM_LOCALID.

Testing

• uv run pytest tests/test_frontend_topology.py tests/test_endpoint_allocation.py

[codecov-commenter]

Codecov Report

❌ Patch coverage is 61.53846% with 10 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (sa-submission-q2-2026@fdb1be7). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/srtctl/cli/mixins/worker_stage.py	11.11%	8 Missing ⚠️
src/srtctl/backends/trtllm.py	0.00%	1 Missing ⚠️
src/srtctl/backends/vllm.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@                   Coverage Diff                    @@
##             sa-submission-q2-2026     #143   +/-   ##
========================================================
  Coverage                         ?   61.04%           
========================================================
  Files                            ?       48           
  Lines                            ?     4161           
  Branches                         ?        0           
========================================================
  Hits                             ?     2540           
  Misses                           ?     1621           
  Partials                         ?        0           

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