refactor: correlate lineage by request ID

[hallerite]

Summary

• replace the eight-field model-request lineage envelope from feat: publish ACP lineage provenance #149 with one opaque X-ACP-Lineage-Request-ID
• keep Idempotency-Key as independent retry/idempotency transport behavior; nano-RLM currently gives it the same stable request ID
• make the ACP ai.prime.acp/lineage-v1 manifest the sole owner of session, context, compaction, ancestry, and request-kind structure
• simplify LineageTracker.start_request() to return the request ID that correlates each model call with manifest.requests

This keeps complete provenance for finished ACP traces while removing duplicated graph data from every provider request. It is the nano-RLM producer half of the request-ID join in verifiers #2452, stacked on PrimeIntellect-ai/verifiers#2449.

Validation

• uv run pytest tests/: 144 passed
• focused lineage/ACP/config/supervisor suite: 37 passed
• two live Prime SWE-bench Verified rollouts through verifiers #2452 passed with two concurrent child sessions and one completed compaction each; every one of the 7 model calls per rollout joined exactly to the 7-request ACP manifest
• ruff check, ruff format, markdownlint, and pre-commit: passed