Add stash recovery support

[dinakars777]

Description

Add support for viewing and recovering git stashes through the TUI.

Suggested Implementation

• Add a toggle mode to switch between reflog and stash view (press s)
• Parse git stash list output
• Display stashes with descriptions and timestamps
• Allow applying/popping stashes with Enter

Technical Details

• Add ViewMode enum (Reflog, Stash)
• Implement git stash list --format=... parsing
• Add stash-specific actions (apply, pop, drop)
• Update UI to show current mode

Why This is a Good First Issue

• Similar pattern to existing reflog parsing
• Clear user value
• Well-defined scope
• Can reuse existing UI components

Related to roadmap item: Stash recovery