feat(sdk): add history-free repository snapshots

[necolas]

Why

Applications need a supported way to create a repository from a selected source tree without copying the source commit history. The snapshot API provides that backend behavior, but the SDKs did not expose its request contract.

Scope

• Add history-free snapshot creation types to the TypeScript, Python, and Go SDKs.
• Send the snapshot source, selected ref, read-scoped source token, and initial root-commit metadata through each SDK.
• Preserve the existing repository creation paths and default the snapshot branch to main when no branch is provided.
• Document the SDK contract, examples, and Git LFS behavior in each package and in the Code Storage agent reference.

Tradeoffs

• Snapshot creation copies Git LFS pointer files, but it does not copy the external LFS objects.

Blast Radius

• This is an additive public SDK change in the TypeScript, Python, and Go packages.
• Existing fork, GitHub sync, and generic Git sync creation behavior remains unchanged.

Verification

• pnpm --filter @pierre/storage build
• pnpm --filter @pierre/storage exec vitest --run (204 tests passed)
• ./venv/bin/python -m pytest -v (184 tests passed)
• ./venv/bin/python -m ruff check pierre_storage
• ./venv/bin/python -m ruff format --check pierre_storage
• go test ./...
• python3 scripts/sync_versions.py --check
• git diff --check dev...HEAD

No live service credentials were required for these checks.

[notion-workspace]

SDK: Support create_repo snapshots