refactor(repo): isolate cumulative xv6 source tree

Move the upstream-derived kernel and user-space sources into xv6/, restore the repository-level task runner, and retarget CI and verification tooling to the clean layout.

Co-authored-by: Meraj PourHosseiny <169587609+MerajPoorhosseiny@users.noreply.github.com>

Co-authored-by: Ali Sadeghi <168981958+Alisssaaaddd@users.noreply.github.com>

Author: mragetsars

.gitignore

@@ -1,22 +1,22 @@
-*~
-_*
-*.o
-*.d
-*.asm
-*.sym
-*.img
-vectors.S
-bootblock
-entryother
-initcode
-initcode.out
-kernel
-kernelmemfs
-mkfs
-.gdbinit
+# xv6 build artifacts
+xv6/*.o
+xv6/*.d
+xv6/*.asm
+xv6/*.sym
+xv6/_*
+xv6/bootblock
+xv6/entryother
+xv6/initcode
+xv6/kernel
+xv6/kernelmemfs
+xv6/mkfs
+xv6/vectors.S
+xv6/*.img
+xv6/.gdbinit
+xv6/dist/
+xv6/dist-test/
 
-dist/
-dist-test/
+# Repository tooling
 __pycache__/
 *.py[cod]
 artifacts/