Feature: Support soft resets and checkouts (non-destructive modes)

[dinakars777]

Currently, pressing Enter performs a git reset --hard, which is totally destructive if you have uncommitted changes you forgot about.

We should add alternative keybindings for safer operations:

• Press s for git reset --soft (keeps working tree intact)
• Press c for git checkout <hash> (puts you in a detached HEAD state to look around)

Implementation thoughts:

• Should be pretty straightforward by duplicating the current Command::new("git") logic and mapping it to the new Crossterm keys in src/main.rs.
• Need to update the footer/help text to display these options.