feat(memory): introduce .claude/{tasks,memory,audits}/ governance layout

Move tasks/ into .claude/tasks/ and create .claude/memory/ with 5
persistent registries (decisions/learnings/blockers/journal/evals) plus
.claude/audits/ for audit reports. Also seed templates/memory/ for
onboarder to copy into user projects.

- tasks/TODO.md, tasks/rtk-upstream-issue.md → .claude/tasks/
- tasks/LESSONS.md deleted (empty template; superseded by learnings.md)
- .claude/memory/: 5 append-only registries with YAML schema + seed entries
- templates/memory/: 5 empty-index templates for new projects

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

templates/memory/decisions.md

@@ -0,0 +1,39 @@
+---
+type: decisions_registry
+entry_prefix: BDR
+schema:
+  id: BDR-XXX
+  date: YYYY-MM-DD
+  title: string (<= 80 chars)
+  decision: string (what was chosen)
+  why: string (motivation, context)
+  alternatives: list of strings (what was rejected + why)
+  status: [proposed | accepted | deprecated | superseded]
+  supersedes: BDR-XXX (optional)
+rules:
+  - Append-only. Never rewrite past entries - add a new one with status superseded if needed.
+  - One entry per non-trivial choice. Trivial = reversible in under 10 min with no cross-file impact.
+  - Capture why more carefully than what - the what rots, the why lasts.
+---
+
+# Decisions registry (BDR)
+
+## Index
+
+| ID | Date | Title | Status |
+|----|------|-------|--------|
+
+<!-- Append entries below. Template:
+
+## BDR-XXX - <titre>
+
+- **Date** : YYYY-MM-DD
+- **Statut** : proposed | accepted | deprecated | superseded
+- **Décision** : <ce qui a été choisi>
+- **Pourquoi** : <motivation>
+- **Alternatives rejetées** :
+  - Option A - <raison du rejet>
+  - Option B - <raison du rejet>
+- **Référence** : <commit / PR / fichier>
+
+-->