chore: bump v2.0.0-alpha.21 (#54)

Fecha a release da sprint de redução de tokens (#47-#53): fda_sdlc enxuto,
rotação de sessão, orçamentos de tokens/timeout, reviewer escopado, tree-guard
compartilhado, /goal por milestone e phase_overrides pré-semeados.


Claude-Session: https://claude.ai/code/session_01NPYaKxNaVRhPumKbawFNT3

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: elberrd

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "impactus",
-  "version": "2.0.0-alpha.20",
+  "version": "2.0.0-alpha.21",
   "description": "IMPACTUS CLI — the IAI installer: agent harness + FIA (the IAI Agent Factory) with Pi, deterministic FDAs and Claude/Codex subscription auth.",
   "type": "module",
   "bin": {