fix(git): propagate exit codes in push/pull/fetch/stash/worktree

[polaminggkub-debug]

Problem

`rtk git push`, `rtk git pull`, `rtk git fetch`, `rtk git stash` (pop/apply/drop/push/default), and `rtk git worktree` all print a `FAILED:` message on error but return exit code 0 to the caller.

This breaks CI/CD pipelines and shell scripts that rely on exit code semantics:

```bash
rtk git push || handle_error # handle_error never called
rtk git pull && deploy # deploy runs even on pull failure
```

Root cause

The failure branches in these functions print the error but fall through to `Ok(())` instead of propagating git's exit code via `std::process::exit()`.

Fix

Add `std::process::exit(output.status.code().unwrap_or(1))` in each failure branch, matching the pattern already used correctly in `run_log`, `run_diff`, `run_add`, and `run_branch`.

Per the Rust docs, `status.code()` returns `Option` — `None` when the process was killed by a signal (Unix). The `.unwrap_or(1)` fallback handles that case correctly.

Functions fixed

Function	Issue
`run_push`	Falls through to `Ok(())` on failure
`run_pull`	Falls through to `Ok(())` on failure
`run_fetch`	Explicit `return Ok(())` on failure
`run_stash` (pop/apply/drop/push)	Falls through to `Ok(())` after timer
`run_stash` (default)	Falls through to `Ok(())` after timer
`run_worktree`	`return Ok(())` on both success and failure

Testing

All 412 existing tests pass. No new behavior on the success path.

🤖 Generated with Claude Code