starkernel: item 4.4e -- fix console_putc() forwarding \n to vt100_putc() without \r

console_putc() mirrored raw '\n' to vt100_putc() while raw_putc() (serial
path) auto-injects '\r' before '\n'. vt100_putc()'s '\n' handler only
increments the row, never resets the column, so every line after the first
started at whatever column the previous line ended on instead of column 0 --
confirmed by screendump as diagonal text scatter across the framebuffer.
Latent since this code was written; invisible until 4.4c turned the
framebuffer console on for the first time.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/starkernel/hal/console.c

@@ -230,6 +230,7 @@ void console_putc(char c) {
 
     /* --- framebuffer VT100 path (when available) --- */
     if (fb_is_available()) {
+        if (c == '\n') vt100_putc('\r');
         vt100_putc(c);
     }
 }