refactor: improve AssumeRoleActivity code quality (CRAP/DRY/SOLID)

- Extract validateAssumeRoleInput() - CRAP ~2
- Extract resolveAssumeRoleConfig() with getOrEnv() helper - CRAP ~4
  * Fixes DRY violation (config resolution was repeated 3x)
- Extract requestAuthToken() - CRAP ~4 (sequential, easy to test)
- Extract buildAssumeRoleOutput() - CRAP ~1
- Main AssumeRoleActivity now ~CRAP 3 (orchestrates high-level flow)

Overall CRAP reduction: 40+ → 6-8 total complexity

Improves:
- Single Responsibility: Each function does one thing
- DRY: Config resolution centralized
- Testability: Each step independently unit-testable
- Readability: Main function reads like pseudocode

k8s/git-commit.yaml

@@ -9,6 +9,6 @@ metadata:
     app.kubernetes.io/name: poimen
     app.kubernetes.io/component: orchestrator
 data:
-  GIT_COMMIT: "f6c6aa03"  # Updated automatically by CI/CD
+  GIT_COMMIT: "cdb6efe2"  # Updated automatically by CI/CD
   GIT_BRANCH: "main"
   DEPLOYMENT_DATE: "2026-09-04"