Refactor git operations: move pull to branches, add status indicators, and improve UX

Major improvements to git operations UI and user experience:

**Git Operations Restructure:**
- Move pull functionality from commit view to branch view (pull only makes sense for branches)
- Remove 'p' key from commit list mode, add to branch list mode with validation
- Only allow pull when branch has commits behind (prevents unnecessary operations)

**Branch Status Indicators:**
- Add ahead/behind commit indicators (/) next to each branch
- Show 2 for branches 2 commits ahead, 3 for 3 commits behind
- Display combined status like 12 for diverged branches
- Fetch remote refs automatically to ensure accurate status

**Real-time Operation Feedback:**
- Add branch-specific animations during push/pull operations
- Show Pushing

ncurses_diff_viewer.c

@@ -3269,7 +3269,7 @@ int handle_ncurses_diff_input(NCursesDiffViewer *viewer, int key) {
     switch (key) {
     case 27: // ESC
       viewer->current_mode =
-          NCURSES_MODE_COMMIT_LIST; // Return to commit list mode
+          NCURSES_MODE_COMMIT_LIST; // Return to commit list mode.
       break;
 
     case KEY_UP: