[Stage 0.5] Create and validate the protected v2 development branch

[draedful]

Parent: #310

Goal

Create the long-lived v2 development branch from a main commit that already contains the approved contract, CI, preview, and release baseline.

Scope

• Complete [Stage 0.2] Capture the v1 public package contract #314, [Stage 0.3] Establish independent v1 and v2 CI, preview, and release workflows #313, [Stage 0.6] Document contribution, manual synchronization, and release routing #316, and the pre-creation part of [Stage 0.4] Prepare and verify rulesets for main and v2 #317.
• Review every open pull request targeting main, especially feat: add Playwright page objects #327, and explicitly decide whether it must:
  • merge before the v2 split;
  • retarget to v2 after the split;
  • close without inclusion.
• Use the starting commit approved in Stage 0.1.
• Confirm that the starting commit contains:
  • the v1 contract fixture;
  • CI routing for main and v2;
  • distinct preview routing;
  • independent v1 and v2 release workflows;
  • contribution, manual synchronization, and release routing documentation.
• Create v2 from that exact main commit.
• Keep main as the default, stable, maintenance-only v1 branch.
• Do not create release/v1.
• Verify that the prepared ruleset applies immediately to v2.
• Verify required checks on v2.
• Verify that release-v2.yml watches v2, cannot update latest, and is ready for 2.x prereleases under next.
• Record the initial common commit between main and v2.
• Route monorepo migration and other v2-only pull requests to v2.

Acceptance criteria

• v2 points to the approved starting commit.
• The starting commit contains the complete Stage 0 delivery baseline.
• Every open pull request targeting main has a recorded merge-before-split, retarget, or close decision.
• main remains the default branch and retains its stable v1 role.
• release/v1 has not been created prematurely.
• The v2 ruleset and required checks are effective.
• The v2 preview route is distinct from the main preview.
• release-v2.yml targets v2, permits only 2.x prereleases, and uses next.
• The initial common commit is recorded.
• Stage 1 is authorized to run on v2.