fix: fall back to git CLI when simple-git fails to detect branch

[BeedZiBood]

Summary

Fixes #1039.

SimpleGit.branchInfo() relies on simple-git's status parser to populate current and tracking. In some setups that parser silently returns null for both even when the branch and its upstream are correctly configured. The values then get propagated as undefined to the non-null-asserted call sites in pull():

const localCommit = await this.git.revparse([branchInfo.current!]);
// ...
const upstreamCommit = await this.git.revparse([branchInfo.tracking!]);

undefined ends up serialized into the spawn args and git fails with:

fatal: ambiguous argument 'undefined': unknown revision or path not in the working tree.

This matches every report in #1039 (same stack through attemptRemoteTask → handleTaskData → plugin task.error → throw).

Fix

In branchInfo(), fall back to data sources that don't depend on git status --porcelain -b -u --null parsing:

• current — use branches.current from the git branch --no-color call that's already made in the same function.
• tracking — call the existing getLocalBranchUpstream(current) helper, which runs git rev-parse --abbrev-ref <branch>@{upstream}.

Both fallbacks only kick in when status returns null, so the happy path is unchanged.

Test plan

• pnpm tsc (no errors)
• pnpm prettier --check on the touched file
• pnpm eslint on the touched file
• Manually verified on an affected vault: before — every commit-and-sync produced Error: undefined / fatal: ambiguous argument 'undefined'; after — pull/sync runs cleanly and reports Pull: Everything is up-to-date / Pulled N files from remote.