refactor(storage): centralize sanitized Git subprocess execution

[seekskyworld]

Fixes #4929

Summary

• add a storage-local Git execution helper for text and byte output
• centralize repository environment sanitization and retain explicit temporary index support
• migrate worktree, workspace identity, and project catalog Git calls

Motivation

Repeated subprocess setup could diverge across security-sensitive Git calls. A single helper keeps repository selection isolated from ambient Git variables while preserving existing timeouts, buffer limits, and error behavior.

Validation

• npm --workspace @maka/core run build
• npm --workspace @maka/storage run build
• npx biome check (changed files)
• git diff --check
• node --test packages/storage/dist/tests/git-exec.test.js packages/storage/dist/tests/git-worktree-child-executor.test.js packages/storage/dist/tests/workspace-identity.test.js packages/storage/dist/tests/project-catalog.test.js (45 passed)

[Astro-Han]

Reviewed exact head 1feaf39d00b1286eb441afbecf1979e82d701cbe.

I found no P0-P3 correctness, ownership, race, repository-selection, timeout, or temporary-index issue in the five-file diff. packages/storage/src/git-exec.ts:20-80 preserves the prior timeout and buffer behavior, isolates Git from ambient repository variables, and retains explicit temporary-index support. The worktree executor, project catalog, and workspace identity callers use the helper with their previous limits; the new test covers both text and byte output with invalid ambient Git variables.

The exact-head hosted label and test checks passed, and the merge-tree and diff check are clean. I could not run the local Storage typecheck because this checkout has no usable tsc, and I did not run an additional Windows smoke test. The refactor/product decision remains for human maintainers; this is a technical review only.

Automated review notice: This is an AI-assisted review and does not replace independent human review.