phase5: closeout — research-forks case study, docs chapter, roadmap + CLAUDE.md

Phase 5 write-up for the two SPEC §13 forks now that both are built:
  - results/phase5/README.md — the full argument for each fork, with the
    kernel-lane demo and learned-policy ranking tables and reproduce commands.
  - results/phase5/learned-policy.txt — captured `cargo run -p policy` output
    over the 34-row ledger.
  - docs/src/research-forks.md — new mdBook chapter, wired into SUMMARY.md.
  - docs/src/roadmap.md — Phase 5 row added; the Frontier section rewritten
    from "out of scope" to "built, both routed to human review", with the
    honest note that the actual GPU run needs GPU hardware absent here.
  - CLAUDE.md — Phase 5 COMPLETE status paragraph.

No trust-layer or gate change; this is documentation of work already
committed (learned policy b7297ad, kernel lane 5abeb60).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EcKPWQ3MQD4NdEHwar96u2

docs/src/SUMMARY.md

@@ -19,6 +19,7 @@
 - [The caught false-accept (comrak)](./case-studies/comrak-false-accept.md)
 - [cJSON — the cross-language proof (C)](./case-studies/cjson.md)
 - [Services & scale: latency under load](./case-studies/service.md)
+- [Research forks: kernel lane & learned policy](./research-forks.md)
 
 # Reference