Post-merge housekeeping after PR #1 (e468d2e) put VR1 Stage 1+2 on main.

- Workflow doc: the Stage 2 "branch merge point" note now records the merge as DONE
  (PR #1, e468d2e) and GENERALIZES it into a standing rule in the Cross-cutting
  discipline section -- "branch-per-stage + MERGE AT STAGE CLOSE": every stage
  develops on its own branch and merging it to main (merge commit, operator-gated)
  is part of that stage's definition-of-done, then the branch is retired. main is
  trunk-of-record only for merged stages; the next stage branches off post-merge main.
- session-ledger: Stage 2 CLOSED+MERGED recorded; the PINNED merge ruling graduated
  into the standing discipline; NEXT = Stage 3 on dc-dc-stage3-phase2-dc-substrate,
  with D-119 selectors + creds-audit (SEC-009) in place.
- Removed temp/ (3 stray screenshot PNGs that rode onto main via 95f0634).

repo-lint 0 fail. No script/harness touched (gauntlet unaffected).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015WgVrZE2ryY9aXP7JiBuwj