refactor: standardize level names across all roles (#195 phase 1)

Rename levels to use consistent industry-standard terminology:
- dev: medior → mid
- qa: reviewer → mid, tester → junior, add senior level
- architect: opus → senior, sonnet → junior

Add backward-compatible migration for projects.json and openclaw.json
config via level aliases in selectors and projects parser.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/roles/index.ts

@@ -13,6 +13,8 @@ export {
   isValidRole,
   getRole,
   requireRole,
+  // Level aliases
+  canonicalLevel,
   // Levels
   getLevelsForRole,
   getAllLevels,