feat(TextInput): Manejar teclas especiales internamente

El widget TextInput ahora procesa internamente:
- Backspace/Delete: borrar caracteres
- Flechas izq/der: mover cursor
- Home/End: inicio/fin del texto
- Shift+movimiento: selección
- Ctrl+A: seleccionar todo
- Enter: submit

Esto hace que el widget sea auto-contenido y reutilizable,
sin requerir manejo de teclas en la aplicación.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/widgets/text_input.zig

@@ -278,8 +278,39 @@ pub fn textInputRect(
     const inner = bounds.shrink(config.padding);
     if (inner.isEmpty()) return result;
 
-    // Handle text input if focused
+    // Handle keyboard input if focused
     if (state.focused and !config.readonly) {
+        // Handle special keys (navigation, deletion)
+        for (ctx.input.key_events[0..ctx.input.key_event_count]) |key_event| {
+            if (key_event.pressed) {
+                const shift = key_event.modifiers.shift;
+                switch (key_event.key) {
+                    .backspace => {
+                        state.deleteBack();
+                        result.changed = true;
+                    },
+                    .delete => {
+                        state.deleteForward();
+                        result.changed = true;
+                    },
+                    .left => state.cursorLeft(shift),
+                    .right => state.cursorRight(shift),
+                    .home => state.cursorHome(shift),
+                    .end => state.cursorEnd(shift),
+                    .enter => {
+                        result.submitted = true;
+                    },
+                    .a => {
+                        // Ctrl+A = Select All
+                        if (key_event.modifiers.ctrl) {
+                            state.selectAll();
+                        }
+                    },
+                    else => {},
+                }
+            }
+        }
+
         // Handle typed text
         const text_in = ctx.input.getTextInput();
         if (text_in.len > 0) {