conio: switch cursor get/set to BIOS calls, rename text-mode accessors

_get_cursor/_set_cursor now use BIOS GetCursor/SetCursor (RST 8, 08Eh/084h)
instead of ESTEX CURSOR/LOCATE; cursor position packed into a two_bytes
union. get_videotextmode/set_videotextmode renamed to gettextmode/settextmode.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

libc/include/conio.h

@@ -74,12 +74,24 @@ uint16_t getkey(void);
 #define KEY_PGUP   0x59
 #define KEY_INS    0x50   /* numpad 0; not verified */
 #define KEY_DEL    0x55   /* numpad 5/.; not verified */
+
+typedef union {
+    uint16_t value;
+    struct {
+        uint8_t low;
+        uint8_t high;
+    } byte;
+} two_bytes;
+
+
+
 char putch (char c);
 char cputs (const char *s);
 int  cprintf(const char *fmt, ...);
 void clrscr(void);
 void gotoxy(uint8_t x, uint8_t y);
 
+
 /* Solid-C compatibility helpers. */
 #define home()       gotoxy(0, 0)
 #define inp(port)    z80_inp(port)
@@ -124,8 +136,8 @@ void clrscr_attr(uint8_t attr);
 #define TEXT_MODE_40x32  0x02
 #define TEXT_MODE_80x32  0x03
 
-uint8_t get_videotextmode(void);
-int     set_videotextmode(uint8_t mode);  /* 0 OK, -1 + errno on bad mode */
+uint8_t gettextmode(void);
+int     settextmode(uint8_t mode);  /* 0 OK, -1 + errno on bad mode */
 
 /* ------------------------------------------------------------------ *
  * Text-output attribute (used by the conio set: putch / cputs / cprintf).