Fix Git sync when server-spawned Git needs SSH or credential-helper env

[ron-ulitsky]

Git auto-sync now preserves the environment Git needs to authenticate when the server fetches or pushes a repository.

The server previously spawned Git with a small environment. That worked for token-backed HTTPS paths, but it broke remotes that depend on the user's home directory, SSH agent, or credential-helper environment. On Windows with an SSH remote, ok sync and editor sync could fail with:

fatal: Could not read from remote repository.

The same git fetch or git push worked from a terminal.

This change keeps the user/home/session variables Git uses to locate SSH keys, SSH agents, and credential helpers. Commit author/committer overrides now merge into that preserved environment, so auto-save commits do not drop auth state before push.

GIT_TERMINAL_PROMPT=0 and locale-stable stderr behavior stay unchanged. GIT_SSH_COMMAND still does not pass through without simple-git's explicit unsafe opt-in.

Testing:

• npx -y bun@1.3.13 test packages/server/src/git-handle.test.ts
• git diff --check
• Fresh Linux container clone of this branch:
  • bun install --frozen-lockfile
  • bun run lint

Manual verification on Windows:

• reproduced the failure with a stripped server-style Git environment
• rebuilt this branch and verified ok sync --json succeeds against an SSH remote
• confirmed sync returns to idle with consecutiveFailures: 0

Notes:

• bun run check in a fresh Linux container hit existing upstream failures. The same sync-engine.test.ts failures reproduce on inkeep/open-knowledge@main, so they are not introduced by this branch.

[CLAassistant]

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[github-actions]

I could not sync this public PR into agents-private automatically.

Patch application failed. The diff could not be applied cleanly. Try rebasing your PR on the latest base branch.

Falling back to direct application...
Applied patch to 'public/open-knowledge/packages/server/src/git-handle.test.ts' cleanly.
Applied patch to 'public/open-knowledge/packages/server/src/git-handle.ts' with conflicts.
Applied patch to 'public/open-knowledge/packages/server/src/sync-engine.ts' with conflicts.
U public/open-knowledge/packages/server/src/git-handle.ts
U public/open-knowledge/packages/server/src/sync-engine.ts