Rename Schunix to SchOS; the kernel becomes SchIFT

Removes the "-unix" element and with it any trademark exposure to The
Open Group.

The split follows the ecosystem layout: SchOS is the system, and the
kernel has its own name. Kernel-identity strings are the only places
that take SchIFT -- uname(2) sysname, /proc/version, and the two licence
sentences that say "kernel" outright. That is what every Unix does here:
`uname -s` on Linux reports the kernel, not the distribution. Everything
a user reads as the product -- panic screen, boot menu, error prefixes,
docs, LICENSE, NOTICE -- is SchOS.

schunix.img is schos.img, the logo assets and the musl TLS patch are
renamed, and __SCHUNIX__ is __SCHOS__ (the define and the patch that
consumes it moved together).

Two things the rename broke, both found by the bootcheck suite:

  - shmtest wrote "SCHUNIX-MMAP-OK" with a hardcoded length of 15 and
    compared it back by hand-counted offsets (m[3]=='U', m[14]=='K').
    The shorter marker left the write running two bytes past the literal
    and the compare reading past the data, failing a file-backed mmap
    that was working correctly. Now written and compared through one
    constant with sizeof.
  - bootcheck asserted a 31-byte file after appending to
    "hello-from-schunix"; the shorter string makes it 29.

Both are the same mistake: a string literal whose length is written out
somewhere else. Full suite green -- base, Tty, Ps, Sock, Fb, Usb, Evdev.

kernel/dev/device.c

@@ -281,7 +281,7 @@ text_selftest(void)
   int line = f->ops->height(f) + 6;
   int y = 80;
 
-  text_draw(&s, f, 60, y + base, "Schunix text rendering", SCH_FG);
+  text_draw(&s, f, 60, y + base, "SchOS text rendering", SCH_FG);
   y += line * 2;
 
   // Deliberately not on a multiple of eight. On the old console this string

kernel/dev/fb.c

@@ -179,7 +179,7 @@ fb_ioctl(int request, addr_t arg)
     if (!f)
       return -EFAULT;
     memset(f, 0, sizeof(*f));
-    safestrcpy(f->id, "schunixfb", sizeof(f->id));
+    safestrcpy(f->id, "schosfb", sizeof(f->id));
     f->smem_start  = (unsigned long)vga_fb_phys();
     f->smem_len    = (unsigned int)vga_fb_size();
     f->type        = FB_TYPE_PACKED_PIXELS;

kernel/dev/procfs.c

@@ -143,7 +143,7 @@ gen_cpuinfo(struct sbuf *sb)
   // otherwise be told a VM with four processors has four to schedule on, when
   // three of them are enumerated and idle. "cpu cores" stays the present count,
   // which is what that field means.
-  // Real values, from CPUID. These used to read "Schunix" and "Schunix virtual
+  // Real values, from CPUID. These used to read "SchOS" and "SchOS virtual
   // CPU" -- a thing to print when you have not asked the processor, and
   // actively unhelpful, because identifying the machine is the one question
   // /proc/cpuinfo exists to answer.
@@ -204,7 +204,8 @@ gen_cpuinfo(struct sbuf *sb)
 static void
 gen_version(struct sbuf *sb)
 {
-  sb_puts(sb, "Schunix version 0.1.0 (schunix) #1 SMP x86_64\n");
+  // The kernel's name, not the system's -- same as "Linux version 6.x" here.
+  sb_puts(sb, "SchIFT version 0.1.0 (schift) #1 SMP x86_64\n");
 }
 
 static void

kernel/dev/ttf.c

@@ -200,7 +200,7 @@ load_outline(struct ttf *f, int gid, struct outline *o)
   // A negative contour count means a composite: the glyph is other glyphs
   // placed at offsets. This is not an exotic case to skip -- `i` is built from
   // a dotless i plus the dot, so skipping composites loses a letter from
-  // "Schunix", which is exactly how the gap was found.
+  // "SchOS", which is exactly how the gap was found.
   //
   // Only the translated case is handled: components with a scale or a 2x2
   // matrix are rare outside of synthesised obliques, and applying a transform

kernel/dev/uart.c

@@ -41,7 +41,7 @@ uartearlyinit(void)
 
 
   // Announce that we're here.
-  for(p="Schunix UART...\n"; *p; p++)
+  for(p="SchOS UART...\n"; *p; p++)
     uartputc(*p);
 }