feat: add CC2 source reconstruction helper

[albertoelopez]

Summary

• adds scripts/reconstruct_cc2_source.py to rebuild a local CC2 source bundle from live GitHub API data when the frozen .omx source inputs are absent
• writes required plans/ and research/ shape plus a reconstruction manifest that explicitly marks the bundle as non-frozen
• adds unit tests for source-bundle shape and JSON parsing

Test Plan

• python3 -m unittest tests.test_cc2_source_reconstruction -v
• python3 scripts/reconstruct_cc2_source.py --out-root /tmp/cc2-reconstructed-source/.omx
• CC2_SOURCE_OMX=/tmp/cc2-reconstructed-source/.omx python3 scripts/generate_cc2_board.py --out-dir /tmp/cc2-reconstructed-board
• python3 scripts/validate_cc2_board.py --board /tmp/cc2-reconstructed-board/board.json
• python3 -m unittest discover -s tests -v
• python3 -m py_compile scripts/reconstruct_cc2_source.py scripts/generate_cc2_board.py scripts/validate_cc2_board.py
• git diff --check

Notes

This helper is intentionally a recovery/local-generation path. It does not claim to recreate the original frozen approved-plan evidence bundle.

[albertoelopez]

Maintainer merge request: this PR is currently mergeable and has no reported failing checks. I attempted to merge it, but GitHub returned a permission error for my account (albertoelopez does not have the correct permissions to execute MergePullRequest). Could someone with write access please review/merge when convenient? Test plan is included in the PR body. Note: this helper is intentionally marked as non-frozen recovery evidence, not a replacement for the original approved source bundle.