feat: switch text to UTF-8; add Unicode key events, dead keys & Czech layout; fix numpad navigation; add NumLock support

template/sysroot/include/gui/widgets.hpp

@@ -212,11 +212,7 @@ struct TextBox {
 
         // Draw cursor if focused
         if (focused) {
-            // Measure text up to cursor position for proportional fonts
-            char prefix[256];
-            for (int i = 0; i < cursor && i < 255; i++) prefix[i] = text[i];
-            prefix[cursor < 255 ? cursor : 255] = '\0';
-            int cx = tx + text_width(prefix);
+            int cx = tx + text_width_n(text, cursor);
             draw_vline(fb, cx, ty, fh, cursor_color);
         }
     }
@@ -230,34 +226,35 @@ struct TextBox {
     void handle_key(const montauk::abi::KeyEvent& key) {
         if (!focused || !key.pressed) return;
 
+        char typed[montauk::utf8::MAX_BYTES];
+        int typed_len = montauk::utf8::key_utf8(key, typed);
+
         if (key.ascii == '\b' || key.scancode == 0x0E) {
-            // Backspace
+            // Backspace: remove the whole character before the cursor
             if (cursor > 0) {
-                for (int i = cursor - 1; i < text_len - 1; i++) {
-                    text[i] = text[i + 1];
-                }
-                text_len--;
-                cursor--;
-                text[text_len] = '\0';
+                int start = montauk::utf8::prev_boundary(text, cursor);
+                int n = cursor - start;
+                for (int i = start; i <= text_len - n; i++)
+                    text[i] = text[i + n];
+                text_len -= n;
+                cursor = start;
             }
-        } else if ((unsigned char)key.ascii >= 32
-                   && (unsigned char)key.ascii != 127) {
-            // Printable character
-            if (text_len < 254) {
-                for (int i = text_len; i > cursor; i--) {
-                    text[i] = text[i - 1];
-                }
-                text[cursor] = key.ascii;
-                cursor++;
-                text_len++;
-                text[text_len] = '\0';
+        } else if (typed_len > 0) {
+            // Printable character, inserted as UTF-8
+            if (text_len + typed_len <= 254) {
+                for (int i = text_len; i >= cursor; i--)
+                    text[i + typed_len] = text[i];
+                for (int i = 0; i < typed_len; i++)
+                    text[cursor + i] = typed[i];
+                cursor += typed_len;
+                text_len += typed_len;
             }
-        } else if (key.scancode == 0x4B) {
+        } else if (montauk::nav_scancode(key) == 0x4B) {
             // Left arrow
-            if (cursor > 0) cursor--;
-        } else if (key.scancode == 0x4D) {
+            cursor = montauk::utf8::prev_boundary(text, cursor);
+        } else if (montauk::nav_scancode(key) == 0x4D) {
             // Right arrow
-            if (cursor < text_len) cursor++;
+            cursor = montauk::utf8::next_boundary(text, text_len, cursor);
         }
     }
 };