chore(custodian): add CLAUDE.md and .claude/rules/ orientation files

Registers llm-connect with the Custodian agent system:
- CLAUDE.md: thin @-import index pointing to modular rules
- .claude/rules/session-protocol.md: orient with get_domain_summary("custodian")
- .claude/rules/repo-identity.md: domain=custodian, slug=llm-connect
- .claude/rules/first-session.md, workplan-convention.md, stack-and-commands.md,
  architecture.md, repo-boundary.md, agents.md, scope.md (stubs to fill in)
- session-protocol notes both local (:8000) and CoulombCore bridge (:18000) URLs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/rules/repo-boundary.md

@@ -0,0 +1,8 @@
+## Repo boundary
+
+This repo owns **{PROJECT_NAME}** only. It does not own:
+
+<!-- TODO: List what belongs in adjacent repos, e.g.:
+- SSH key management → railiance-infra/
+- State hub code     → the-custodian/state-hub/
+-->