Fix GTK keybindings: Add fallback handlers and fix init.lua syntax error

This commit fixes keybinding functionality in the GTK4 frontend by adding
fallback handlers for common editing keys and fixing a critical syntax error
in init.lua that prevented all keybindings from loading.

Key Fixes:
- Add fallback handlers for Return, Backspace, and Delete keys
- Return: Insert newline and move to next line
- Backspace: Delete character backward, join lines if at line start
- Delete: Delete character forward
- Enhanced debug output for key event troubleshooting

Critical Bug Fix:
- Remove accidental text "kjjkjlkjm,j;lkjj" from init.lua line 1
- This syntax error prevented init.lua from loading
- All keybindings are now properly registered on startup

Debug Improvements:
- Add debug output for raw keyval and resolved key names
- Show modifier states (Ctrl, Alt, Meta) for each key press
- Enable Key: output to track key processing

Files Modified:
- src/gtk_editor.cpp: Fallback handlers and debug output
- init.lua: Fix syntax error on line 1

Testing:
- All standard keybindings now work (C-n, C-p, C-f, C-b, C-a, C-e, etc.)
- Return creates new lines correctly
- Backspace deletes characters and joins lines
- Theme switching works (C-x t v/e/d)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/gtk_editor.cpp

@@ -248,6 +248,7 @@ protected:
     bool on_key_pressed(guint keyval, guint /*keycode*/, Gdk::ModifierType state) {
         // 1. Resolve the base key name
         std::string key_name = resolve_key(keyval, state);
+        std::cout << "[DEBUG] Raw keyval: " << keyval << ", resolved to: '" << key_name << "'" << std::endl;
         if (key_name.empty()) return false;
 
         // 2. Handle Modifiers
@@ -257,6 +258,9 @@ protected:
         bool is_meta = (state_uint & static_cast<unsigned int>(Gdk::ModifierType::META_MASK)) != 0;
         bool is_lumacs_meta = is_alt || is_meta;
 
+        std::cout << "[DEBUG] Modifiers - Ctrl: " << is_control << ", Alt: " << is_alt
+                  << ", Meta: " << is_meta << std::endl;
+
         // 3. Handle Minibuffer Input Logic (Command/Buffer/File modes)
         // If in a special mode, we might consume the key directly instead of passing to Lua bindings,
         // UNLESS it's a control sequence like C-g or Return.
@@ -317,15 +321,41 @@ protected:
         if (is_control && key_name.length() == 1) key_name = "C-" + key_name;
         if (is_lumacs_meta) key_name = "M-" + key_name; // Use combined meta/alt
 
-        // std::cout << "Key: " << key_name << std::endl;
+        std::cout << "Key: " << key_name << std::endl; // Enable debug output
         KeyResult result = core_->lua_api()->process_key(key_name);
 
-        // Fallback: Insert printable characters if unbound
-        if (result == KeyResult::Unbound && key_name.size() == 1 &&
-            key_name[0] >= 32 && key_name[0] <= 126) {
-            auto cursor = core_->cursor();
-            core_->buffer().insert_char(cursor, key_name[0]);
-            core_->set_cursor({cursor.line, cursor.column + 1});
+        // Fallback handlers for common editing keys
+        if (result == KeyResult::Unbound) {
+            // Return - insert newline
+            if (key_name == "Return") {
+                auto cursor = core_->cursor();
+                core_->buffer().insert_newline(cursor);
+                core_->set_cursor({cursor.line + 1, 0});
+            }
+            // Backspace - delete character
+            else if (key_name == "Backspace") {
+                auto cursor = core_->cursor();
+                core_->buffer().erase_char(cursor);
+                if (cursor.column > 0) {
+                    core_->set_cursor({cursor.line, cursor.column - 1});
+                } else if (cursor.line > 0) {
+                    // Join with previous line
+                    const auto& prev_line = core_->buffer().line(cursor.line - 1);
+                    size_t prev_line_len = prev_line.length();
+                    core_->set_cursor({cursor.line - 1, prev_line_len});
+                }
+            }
+            // Delete - delete character forward
+            else if (key_name == "Delete") {
+                auto cursor = core_->cursor();
+                core_->buffer().erase_char({cursor.line, cursor.column + 1});
+            }
+            // Insert printable characters if unbound
+            else if (key_name.size() == 1 && key_name[0] >= 32 && key_name[0] <= 126) {
+                auto cursor = core_->cursor();
+                core_->buffer().insert_char(cursor, key_name[0]);
+                core_->set_cursor({cursor.line, cursor.column + 1});
+            }
         }
 
         // Request redraw after processing input