Update CLAUDE.md, ai-assistance-guide, and changelog for new C2 tooling

- CLAUDE.md: add branch naming, commit convention, and --resume to C2 summary
- ai-assistance-guide: add docs-mikado --resume to mise tasks table
- Changelog fragment: cover all new conventions and tooling

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

CLAUDE.md

@@ -39,7 +39,7 @@ Before starting work, classify the change:
 
 **C1** — feature branch with early PR. Search related docs first, write documentation changes before code, deploy from the unmerged branch (ArgoCD `--revision`, Ansible from checkout). Upgrade to C2 if complexity spirals.
 
-**C2** — feature branch governed by the Mikado Branch Invariant: all Mikado card commits come first, then code progress commits, then card-closing commits. Reset the branch when new prerequisites are discovered.
+**C2** — branch `mikado/<chain-stem>` governed by the Mikado Branch Invariant: all card commits first, then code progress, then card closures. Commits use `C2(<chain>): plan/impl/close/finalize` convention. Reset the branch when new prerequisites are discovered. Resume with `mise run docs-mikado --resume`.
 
 See [[agent-change-process]] for the full methodology.
 

docs/changelog.d/formalize-change-classification.doc.md

@@ -1 +1 @@
-Formalize C0/C1/C2 change classification: C0 allows direct-to-main commits, C1 adds docs-first workflow with branch deployment, C2 introduces the Mikado Branch Invariant for strict commit ordering on multi-phase changes.
+Formalize C0/C1/C2 change classification: C0 allows direct-to-main commits, C1 adds docs-first workflow with branch deployment, C2 introduces the Mikado Branch Invariant for strict commit ordering on multi-phase changes. Add C2 conventions: `C2(<chain>): plan/impl/close/finalize` commit messages, `mikado/<chain-stem>` branch naming, and `branch:` frontmatter on goal cards. New tooling: `docs-mikado --resume` for cold-start session pickup and `mikado-branch-invariant-check` pre-commit hook.

docs/tutorials/ai-assistance-guide.md

@@ -89,6 +89,7 @@ BlumeOps operations are driven by mise tasks. Run `mise tasks` to list all avail
 |------|-------------|
 | `ai-docs` | At session start - review infrastructure documentation |
 | `docs-mikado` | View active Mikado dependency chains for C2 changes |
+| `docs-mikado --resume` | Resume a C2 chain: detect branch, show state and next steps |
 | `provision-indri` | Deploy changes to [[indri]]-hosted services via Ansible |
 | `services-check` | After deployments - verify all services are healthy |
 | `pr-comments` | Check unresolved PR comments during review |