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- tasks/LESSONS.md deleted (empty template; superseded by learnings.md)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/learnings.md

@@ -0,0 +1,32 @@
+---
+type: learnings_registry
+entry_prefix: LRN
+schema:
+  id: LRN-XXX
+  date: YYYY-MM-DD
+  pattern: string (what was observed, abstracted)
+  context: string (where/when it happened - concrete)
+  future_application: string (when to recall this)
+rules:
+  - Capture learnings that apply beyond the current task.
+  - Abstract from the incident - the pattern is what is reusable, not the one-shot fact.
+  - Link to source (commit, file, PR) when possible.
+---
+
+# Learnings registry (LRN)
+
+## Index
+
+| ID | Date | Pattern | Applies to |
+|----|------|---------|------------|
+
+<!-- Append entries below. Template:
+
+## LRN-XXX - <pattern abstrait>
+
+- **Date** : YYYY-MM-DD
+- **Pattern** : <ce qui a été observé, formulé de manière réutilisable>
+- **Contexte** : <où et quand, concret>
+- **Application future** : <quand se rappeler de ceci>
+
+-->