Add native TileRT P/D orchestration

[cquil11]

Summary

• add a native TileRT backend for vLLM prefill plus TileRT decode
• add the official tilert.pd_vllm.pd_router frontend with exact static P/D topology
• support role-specific worker images without shell-level Slurm orchestration
• materialize converted decode weights once under a shared lock, with atomic publication and cache reuse
• provide an idempotent role-aware runtime setup for the published TileRT and NIXL versions
• validate the single-router/single-prefill topology and managed command ownership

Stack

This PR is stacked directly on #7, which is stacked on #1. PR #3 remains separate.

Current validation

• 244 focused schema/frontend/backend tests pass
• targeted ty type checking passes
• ruff, formatting, Bash syntax, and diff checks pass
• draft while the InferenceX AgentX port is completed and exercised on B200 infrastructure

[cquil11]

Closing because the project scope is now limited to porting active, nondeprecated AMD multi-node configurations to srt-slurm. This PR is outside that scope.