docs: update contributing guidelines and skill type taxonomy

- Rewrite CONTRIBUTING.md with four skill types (feature, utility,
  operational, container), PR requirements, pre-submission checklist
- Update PR template with skill type checkboxes and docs option
- Add label-pr workflow to auto-label PRs from template checkboxes
- Add hidden template version marker (v1) for follows-guidelines label
- Update CLAUDE.md with skill types overview and contributing instruction
- Update skills-as-branches.md to reference full taxonomy
- Remove /clear from README RFS (already exists as /add-compact)
- Delete obsolete docs (nanorepo-architecture.md, nanoclaw-architecture-final.md)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/label-pr.yml

@@ -0,0 +1,35 @@
+name: Label PR
+
+on:
+  pull_request:
+    types: [opened, edited]
+
+jobs:
+  label:
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
+    steps:
+      - uses: actions/github-script@v7
+        with:
+          script: |
+            const body = context.payload.pull_request.body || '';
+            const labels = [];
+
+            if (body.includes('[x] **Feature skill**'))       { labels.push('PR: Skill'); labels.push('PR: Feature'); }
+            else if (body.includes('[x] **Utility skill**'))   labels.push('PR: Skill');
+            else if (body.includes('[x] **Operational/container skill**')) labels.push('PR: Skill');
+            else if (body.includes('[x] **Fix**'))             labels.push('PR: Fix');
+            else if (body.includes('[x] **Simplification**'))  labels.push('PR: Refactor');
+            else if (body.includes('[x] **Documentation**'))   labels.push('PR: Docs');
+
+            if (body.includes('contributing-guide: v1')) labels.push('follows-guidelines');
+
+            if (labels.length > 0) {
+              await github.rest.issues.addLabels({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                issue_number: context.payload.pull_request.number,
+                labels,
+              });
+            }