refactor: move bundled skills tree to repo root skills/

- Relocate runtime/skills -> skills/; runtime_skills_root() prefers oclaw/skills
  with fallback to legacy runtime/skills for unmigrated trees.
- session-bootstrap hook handler resolves repo root via PROJECT_ROOT.
- Update architecture/migration docs and in-tree skill references.

Co-authored-by: Cursor <cursoragent@cursor.com>

skills/skill-creator/_meta.json

@@ -0,0 +1,6 @@
+{
+  "ownerId": "kn7ajm25k9s5t1ajwxp2yfjx818015pb",
+  "slug": "skill-creator",
+  "version": "0.1.0",
+  "publishedAt": 1769522677376
+}