chore: verify stale sync branches removed & close IPADP Phase 2 milestone

[satwareAG-ironMike]

Context

Housekeeping after the v0.7.3 sync (PR #12) and IPADP L1-L3 metadata landing (PR #13).

Acceptance criteria

• Verify origin/feat/privacy-validation-l2 is deleted (merged via PR feat: IPADP L2 Privacy Validation #11).
• Verify origin/sync/upstream-v0.7.3 is deleted (merged via PR Sync with upstream v0.7.3 (fork agents preserved) #12).
• Verify origin/feature/ipadp-l1-l3-cline-harmony is deleted (merged via PR feat(ipadp): L1-L3 conformance + Cline harmony metadata #13).
• Confirm remote branches on origin are reduced to main, main-speck, and HEAD.
• Close milestone Implementation: Native Cline/Junie Support in Spec-Kit #3 IPADP Phase 2: L2 Privacy Validation (both issues Implement privacy validation script for L2 conformance #9 and Add CI workflow for privacy leak detection #10 are closed; .github/workflows/privacy-check.yml is live on main-speck).

Verification (2026-04-20)

```
$ git branch -r | grep -v upstream
origin/HEAD -> origin/main-speck
origin/main
origin/main-speck

$ gh api repos/satwareAG/spec-kit/milestones/3 --jq '{state,open_issues,closed_issues}'
{"state":"open","open_issues":0,"closed_issues":2}
```

All stale branches are already pruned remotely. The only remaining action is closing milestone #3.

Follow-ups (out of scope for this issue)

Candidates for an upcoming IPADP Phase 3: L3 Upstream Sync Automation milestone:

• Scheduled GitHub Actions workflow wrapping `scripts/bash/check-upstream-sync.sh` to auto-open an issue on new upstream `github/spec-kit` release tags.
• Integrate Cline `sod.protocol.md` / `eod.protocol.md` into repo scripts / daily routine.

[satwareAG-ironMike]

All acceptance criteria verified on 2026-04-20. Stale branches already pruned; closing milestone #3 now.