docs: add MIGRATION.md for existing projects

One-shot bash migration block for repos onboarded before this layout:
creates .claude/{tasks,memory,audits}, moves tasks/*.md + AUDIT_* +
orphan root audits (SEO/GEO/HARDEN/VALIDATE/BUGS-FOUND) to the new
homes, seeds memory registries from templates, patches .gitignore to
un-ignore shared dirs, and ships a post-migration sanity check.

Uses mv throughout (no rm) so the migration stays reversible via
git checkout . until the commit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

MIGRATION.md

@@ -0,0 +1,170 @@
+# Migration guide — `.claude/` restructure (2026-04-23)
+
+The claude-config layout moved task tracking, memory registries, and audit
+reports out of scattered roots (`tasks/`, `SEO.md`, `HARDEN.md`, etc.) into
+a single governance root: `.claude/{tasks,memory,audits}/`.
+
+This guide walks through the migration for **existing projects** that use
+claude-config skills and were onboarded before this change.
+
+---
+
+## TL;DR — full migration in one block
+
+Run from the project root. Inspect the output before committing.
+
+```bash
+# 1. Create the new directory layout
+mkdir -p .claude/tasks .claude/memory .claude/audits
+
+# 2. Move task files
+[ -d tasks ] && {
+  for f in tasks/*.md; do
+    [ -f "$f" ] || continue
+    case "$(basename "$f")" in
+      LESSONS.md)
+        # Deprecated - content goes into learnings.md (see step 3)
+        mv "$f" .claude/tasks/LESSONS.legacy.md
+        ;;
+      AUDIT_GOOD.md|AUDIT_ISSUES.md|AUDIT_PROPOSALS.md|ONBOARD_REPORT.md)
+        mv "$f" ".claude/audits/$(basename "$f")"
+        ;;
+      *)
+        mv "$f" ".claude/tasks/$(basename "$f")"
+        ;;
+    esac
+  done
+  # Remove the empty tasks/ dir if nothing's left
+  rmdir tasks 2>/dev/null
+}
+
+# 3. Move orphan audit reports from project root
+for f in SEO.md GEO.md HARDEN.md VALIDATE.md BUGS-FOUND.md; do
+  [ -f "$f" ] && mv "$f" ".claude/audits/$f"
+done
+
+# 4. Seed the 5 memory registries from the shipped templates
+#    (only if they don't exist yet - never overwrite real content)
+for reg in decisions learnings blockers journal evals; do
+  target=".claude/memory/${reg}.md"
+  src="$HOME/.claude/templates/memory/${reg}.md"
+  if [ ! -f "$target" ] && [ -f "$src" ]; then
+    cp "$src" "$target"
+    echo "✅ Created $target"
+  elif [ -f "$target" ]; then
+    echo "⏭️  Kept existing $target"
+  else
+    echo "⚠️  Template missing: $src"
+  fi
+done
+
+# 5. If LESSONS.legacy.md had useful entries, convert them manually into
+#    .claude/memory/learnings.md (LRN-XXX format) then delete LESSONS.legacy.md
+
+# 6. Update .gitignore - see "Gitignore patch" section below
+
+# 7. Update CLAUDE.md - see "CLAUDE.md patch" section below
+
+# 8. Verify
+git status
+git check-ignore -v .claude/memory/decisions.md .claude/tasks/TODO.md 2>&1
+```
+
+---
+
+## Gitignore patch
+
+If your project's `.gitignore` contains a bare `.claude/` rule, it will ignore
+every memory/tasks/audit file you just created. Replace that line with:
+
+```gitignore
+# Local project config (per-machine)
+.claude/*
+!.claude/tasks/
+!.claude/memory/
+!.claude/audits/
+!.claude/settings.json
+# These stay ignored (per-machine state)
+.claude/settings.local.json
+.claude/agent-memory/
+```
+
+Verify after edit:
+
+```bash
+# These MUST be trackable (exit 1)
+git check-ignore .claude/memory/decisions.md .claude/tasks/TODO.md .claude/audits/
+
+# These MUST still be ignored (exit 0)
+git check-ignore .claude/settings.local.json .claude/agent-memory/
+```
+
+---
+
+## CLAUDE.md patch
+
+If your project's `CLAUDE.md` references `tasks/LESSONS.md` / `tasks/TODO.md`,
+update the `## Session start`, `## Workflow`, `## After code changes`, and
+`## Task tracking` sections to use `.claude/tasks/TODO.md` and reference the
+5 memory registries.
+
+Fastest route: run `/onboard` on the project (safe, won't overwrite existing
+CLAUDE.md — it will merge). Otherwise, apply this diff manually:
+
+```diff
+ ## Session start
+-1. Read `tasks/LESSONS.md` — apply all lessons before touching anything.
+-2. Read `tasks/TODO.md` — understand current state.
+-3. If neither exists, create both before starting.
++1. Read `.claude/memory/` — the 5 registries (decisions, learnings, blockers, journal, evals).
++2. Read `.claude/tasks/TODO.md` — understand current state.
++3. If missing, create from `~/.claude/templates/memory/`.
+```
+
+Add a new section referencing the registries (full template in
+`~/.claude/CLAUDE.md` — copy the `## Memory registries (.claude/memory/)` block).
+
+---
+
+## What gets committed vs ignored
+
+| Path | Committed? | Reason |
+|------|-----------|--------|
+| `.claude/tasks/*.md` | ✅ yes | Shared project backlog |
+| `.claude/memory/*.md` | ✅ yes | Shared decisions/learnings/blockers |
+| `.claude/audits/*.md` | ✅ yes | Snapshot of project state — version-able |
+| `.claude/settings.json` | ✅ yes | Shared project config |
+| `.claude/settings.local.json` | 🚫 no | Per-machine overrides |
+| `.claude/agent-memory/` | 🚫 no | Per-session agent state |
+
+---
+
+## Post-migration sanity check
+
+```bash
+# 1. No legacy tasks/ dir left
+[ -d tasks ] && echo "⚠️ tasks/ still exists" || echo "✅ tasks/ gone"
+
+# 2. No orphan audit files at project root
+for f in SEO.md GEO.md HARDEN.md VALIDATE.md BUGS-FOUND.md; do
+  [ -f "$f" ] && echo "⚠️ $f still at root"
+done
+
+# 3. Structure in place
+ls .claude/tasks .claude/memory .claude/audits
+
+# 4. Git sees the new files as trackable
+git status -u .claude/ --short
+```
+
+All four checks should be clean before committing the migration.
+
+---
+
+## If anything goes wrong
+
+- The migration block only uses `mv`, not `rm` — nothing is deleted.
+- Old `LESSONS.md` is preserved as `LESSONS.legacy.md` — review it, copy
+  meaningful entries into `.claude/memory/learnings.md` (with `LRN-XXX` IDs),
+  then delete.
+- To undo: `git checkout .` before commit.