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/tiers.ts

@@ -4,7 +4,7 @@
  * This module now delegates to the centralized role registry (lib/roles/).
  * Kept for backward compatibility — new code should import from lib/roles/ directly.
  *
- * Level names are plain: "junior", "senior", "reviewer", etc.
+ * Level names are plain: "junior", "mid", "senior".
  * Role context (dev/qa/architect) is always provided by the caller.
  */
 import {