Add /retrofit command for Part 3 of the playbook

Automate the per-project retrofit (git audit, verify, scope, commit,
validate) as a main-thread slash command that asks for the judgment
calls. Step 1 (mining a past chat) stays manual — the command surfaces
which conversation to mine and hands back, since it can't resume one.

adapters/claude/commands/retrofit.md

@@ -0,0 +1,25 @@
+---
+description: Per-project retrofit — git audit, then mine/verify/scope/commit/validate a project's brain onto disk (Part 3 of the retrofit playbook)
+argument-hint: [optional notes, e.g. "old chat already mined"]
+allowed-tools: Bash, Read, Edit, Write, Grep, Glob, Agent
+---
+
+Run the per-project retrofit for the repository in the current working directory.
+Optional notes from me (may be empty): $ARGUMENTS
+
+Your complete orchestration guide — the phases, the mining gate you must hand back to me,
+the decisions to ask about, and the final report format — is at:
+
+    ~/Projects/standards/guides/retrofit.md
+
+Read it in full first, then follow it exactly. If you cannot read that file, stop and
+report precisely that — do not improvise the retrofit.
+
+This runs in the main thread on purpose: ask me the judgment calls (which old chat to
+mine, ambiguous command fixes, the whole-repo-vs-subsystem split, commit/push approval)
+and wait — don't guess on anything that lands on disk. You cannot resume a past
+conversation yourself, so when AGENTS.md doesn't exist yet, surface which conversation to
+mine and stop, per Phase 2.
+
+For Phase 5, delegate to the portability-checker and reviewer subagents (the foreground
+is fine; they're read-only).