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

programs/lib/libc/libc.c

@@ -1712,7 +1712,10 @@ static int _stdin_pump(int block) {
     for (;;) {
         int c = block ? (int)_mtk_syscall0(SYS_GETCHAR)
                       : (int)_mtk_syscall0(SYS_GETCHAR_NB);
-        if (c <= 0) {
+        /* The syscall returns a sign-extended char: bytes >= 0x80 arrive
+           negative and are real keys, only 0 means "nothing". */
+        if (c < 0) c &= 0xFF;
+        if (c == 0) {
             if (block) continue;
             return 0;
         }
@@ -1721,12 +1724,26 @@ static int _stdin_pump(int block) {
 
         if (c == '\b' || c == 127) {
             if (_stdin_line_len > 0) {
+                /* Drop the whole UTF-8 character: its continuation bytes,
+                   then the lead byte. One terminal cell either way. */
+                while (_stdin_line_len > 1 &&
+                       ((unsigned char)_stdin_linebuf[_stdin_line_len - 1] & 0xC0) == 0x80)
+                    _stdin_line_len--;
                 _stdin_line_len--;
                 _stdin_echo_char('\b');
             }
             continue;
         }
 
+        /* Bytes >= 0x80 are UTF-8: the kernel encodes typed characters, and
+           piped input is UTF-8 already. They are stored and echoed as-is. */
+        if (c >= 0x80) {
+            if (_stdin_line_len + 2 >= sizeof(_stdin_linebuf)) continue;
+            _stdin_linebuf[_stdin_line_len++] = (char)c;
+            _stdin_echo_char((char)c);
+            continue;
+        }
+
         if (c == '\n') {
             _stdin_linebuf[_stdin_line_len++] = (char)c;
             _stdin_echo_char((char)c);