feat: Add help popup with keyboard shortcuts triggered by "?"

gtm

@@ -145,6 +145,9 @@ class AppState:
     search_query: str = ""
     search_matches: List[int] = field(default_factory=list)  # Line numbers of matches
     current_match_idx: int = -1  # Index in search_matches
+    
+    # Help popup
+    show_help: bool = False
 
 # --- Actions (Controller) ---
 
@@ -646,6 +649,99 @@ def draw_selection(stdscr, state):
         except curses.error:
             pass
 
+def draw_help_popup(stdscr, state):
+    """Draw a popup with keyboard shortcut help."""
+    if not state.show_help:
+        return
+    
+    # Calculate popup dimensions and position
+    popup_width = 60
+    popup_height = 20
+    popup_x = max(0, (state.width - popup_width) // 2)
+    popup_y = max(0, (state.height - popup_height) // 2)
+    
+    # Draw popup border
+    for y in range(popup_y, popup_y + popup_height):
+        for x in range(popup_x, popup_x + popup_width):
+            if y == popup_y or y == popup_y + popup_height - 1:
+                # Top and bottom borders
+                try:
+                    stdscr.addch(y, x, curses.ACS_HLINE)
+                except curses.error:
+                    pass
+            elif x == popup_x or x == popup_x + popup_width - 1:
+                # Left and right borders
+                try:
+                    stdscr.addch(y, x, curses.ACS_VLINE)
+                except curses.error:
+                    pass
+    
+    # Draw corners
+    try:
+        stdscr.addch(popup_y, popup_x, curses.ACS_ULCORNER)
+        stdscr.addch(popup_y, popup_x + popup_width - 1, curses.ACS_URCORNER)
+        stdscr.addch(popup_y + popup_height - 1, popup_x, curses.ACS_LLCORNER)
+        stdscr.addch(popup_y + popup_height - 1, popup_x + popup_width - 1, curses.ACS_LRCORNER)
+    except curses.error:
+        pass
+    
+    # Draw title
+    title = " Keyboard Shortcuts "
+    title_x = popup_x + (popup_width - len(title)) // 2
+    try:
+        stdscr.addstr(popup_y, title_x, title, curses.A_BOLD)
+    except curses.error:
+        pass
+    
+    # Define help content
+    help_items = [
+        ("Navigation", ""),
+        ("j / Down", "Scroll down"),
+        ("k / Up", "Scroll up"),
+        ("Space / Page Down", "Page down"),
+        ("b / Page Up", "Page up"),
+        ("h / Left", "Focus left pane"),
+        ("l / Right", "Focus right pane"),
+        ("", ""),
+        ("Features", ""),
+        ("/ (slash)", "Search in file"),
+        ("n", "Next search match"),
+        ("N", "Previous search match"),
+        ("c", "Next change"),
+        ("C", "Previous change"),
+        ("s", "Toggle sidebar"),
+        ("w", "Toggle line wrapping"),
+        ("L", "Toggle line numbers"),
+        ("q / Esc", "Quit"),
+        ("? (question mark)", "Show/hide this help")
+    ]
+    
+    # Draw help content
+    for i, (key, desc) in enumerate(help_items):
+        y = popup_y + 2 + i
+        if y < popup_y + popup_height - 1:
+            if key == "Navigation" or key == "Features":
+                # Section headers
+                try:
+                    stdscr.addstr(y, popup_x + 2, key, curses.A_BOLD | curses.A_UNDERLINE)
+                except curses.error:
+                    pass
+            elif key:
+                # Key and description
+                try:
+                    stdscr.addstr(y, popup_x + 2, key, curses.A_BOLD)
+                    stdscr.addstr(y, popup_x + 16, desc)
+                except curses.error:
+                    pass
+    
+    # Draw footer
+    footer = " Press any key to close "
+    footer_x = popup_x + (popup_width - len(footer)) // 2
+    try:
+        stdscr.addstr(popup_y + popup_height - 1, footer_x, footer, curses.A_BOLD)
+    except curses.error:
+        pass
+
 def draw_status_bars(stdscr, state):
     # We'll use height-1 for the single status bar
     visible_height = state.height - 1
@@ -780,6 +876,7 @@ def draw_ui(stdscr, state):
     draw_divider(stdscr, state)
     draw_status_bars(stdscr, state)
     draw_selection(stdscr, state)
+    draw_help_popup(stdscr, state)
     stdscr.refresh()
 
 # --- Input Handling Functions (Controller) ---
@@ -972,6 +1069,10 @@ def handle_mouse_input(stdscr, state: AppState) -> AppState:
     return state
 
 def handle_keyboard_input(key, state: AppState) -> AppState:
+    # If help popup is open, any key closes it
+    if state.show_help:
+        return replace(state, show_help=False)
+    
     # If in search mode, handle search input
     if state.search_mode:
         if key == 27:  # Escape key - exit search mode
@@ -993,10 +1094,14 @@ def handle_keyboard_input(key, state: AppState) -> AppState:
     if key in [ord('q')]:
         return replace(state, should_exit=True)
     elif key == 27:  # Escape key
-        if state.is_selecting:
+        if state.show_help:
+            return replace(state, show_help=False)
+        elif state.is_selecting:
             return replace(state, is_selecting=False, selection_start_coord=None, selection_end_coord=None)
         else:
             return replace(state, should_exit=True)
+    elif key == ord('?'):  # Toggle help popup
+        return replace(state, show_help=not state.show_help)
     elif key == ord('/'):  # Start search
         return replace(state, search_mode=True, search_query="")
     elif key == ord('s'):