[chore] Refactor git repos to include aruna V3 into aruna

[St4NNi]

Consolidate the aruna-v3 prototype (https://github.com/arunaengine/aruna-v3) into the main aruna repository (https://github.com/arunaengine/aruna). The current main branch becomes a v2 maintenance branch, and the V3 codebase takes over main for active development.

Workplan

1. Create v2 branch from current main to preserve V2 for ongoing maintenance
2. Graft V3 repository history onto V2's final commit and push to main (commit timestamps are metadata only; parent-child relationships define history)
3. Update CI/CD workflows to support both branches: shared test/codecov logic, separate Harbor push configurations for V2 and V3
4. Rework README for V3: include vision and features, add development disclaimer at the top, and link to the V2 README in the v2 branch
5. Triage existing issues for V3 relevance; relabel or update as needed
6. Archive the standalone aruna-v3 repository with a redirect to main repo

Definition of Done

• v2 branch exists with full V2 history and continues to build/test correctly
• Main branch contains V3 code with complete V3 history grafted onto V2's final commit
• CI/CD runs tests and codecov on both branches
• Harbor push works correctly for V2 and V3 with appropriate tags/targets
• V3 README includes vision, features, development disclaimer, and link to V2 README
• Existing issues triaged and labeled appropriately
• aruna-v3 repository archived

Test Concept

• Verify git log shows continuous history (V2 followed by V3 commits) on main
• Run test suites on both v2 and main branches
• Trigger CI/CD pipelines and confirm correct Harbor push behavior for each branch
• Manual review of README content and links

Risks / Blockers

• CI/CD rework may require significant changes to workflow files if V2 and V3 have different build requirements
• Grafting history rewrites V3 commit hashes, which breaks any external references to those commits
• Issue triage requires manual review to determine V3 relevance