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>

runtime/skills/tushare-finance/_meta.json

@@ -1,6 +0,0 @@
-{
-  "ownerId": "kn7fnx0e4a5kyh3xpffp43fjh5810w1s",
-  "slug": "tushare-finance",
-  "version": "2.0.6",
-  "publishedAt": 1771038127506
-}