legal: bundle third-party licenses on the ISO; stop shipping doom1.wad

- New 0:/os/licenses/ directory on the ISO with GPL-3.0.txt (Flat Remix
  icon theme), GPL-2.0.txt (doomgeneric DOOM engine), and NOTICES.txt
  (mirrors montaukos.org/THIRD-PARTY-NOTICES.txt).
- THIRD-PARTY-NOTICES.txt gains a Flat Remix section (GPLv3, attribution,
  modification and corresponding-source statements; the shipped SVGs are
  the source form).
- man legal now lists third-party components and points at 0:/os/licenses/.
- doom1.wad removed from the repo and the build: the shareware WAD is
  proprietary id Software content. doom.elf (GPLv2) still ships; users
  must supply their own WAD.

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

programs/man/legal.7

@@ -25,4 +25,18 @@
     INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
     LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
     OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
-    PERFORMANCE OF THIS SOFTWARE.
+    PERFORMANCE OF THIS SOFTWARE.
+
+.SH THIRD-PARTY COMPONENTS
+    MontaukOS is distributed together with third-party components that remain
+    under their own licenses, including:
+
+    * Flat Remix icon theme, Copyright (C) Daniel Ruiz de Alegria - GPLv3
+    * DOOM engine (doom.elf, via doomgeneric), Copyright (C) id Software, Inc.
+      and contributors - GPLv2
+    * Limine bootloader, Copyright (C) Mintsuki and contributors - BSD 2-Clause
+    * BearSSL, Copyright (c) Thomas Pornin - MIT
+    * stb_image, Copyright (c) Sean Barrett - MIT
+
+    Full license texts and notices are on this system in 0:/os/licenses/
+    (NOTICES.txt, GPL-2.0.txt, GPL-3.0.txt).