chore: add .gitignore

.gitignore

@@ -0,0 +1,54 @@
+# Build artifacts
+build/
+zig-out/
+.zig-cache/
+nimcache/
+*.o
+*.a
+*.elf
+*.img
+*.bin
+*.log
+
+# Kernel build intermediates
+build_full.log
+current_run.elf
+kernel_cache.elf
+kernel_final.elf
+abi.o
+
+# Nim cache
+build/nimcache/
+build/init_nimcache/
+build/lwip_objs/
+
+# InitRD build outputs (regenerated)
+build/sysro/
+build/initrd.tar
+build/embed_initrd.S
+build/init
+build/head.o
+build/head.S
+build/head_user.o
+build/head_user.S
+build/disk.img
+build/disk_aarch64.img
+build/clib_user.o
+build/dummy.c
+
+# IDE / Editor
+.vscode/
+.idea/
+*.swp
+*.swo
+*~
+
+# OS files
+.DS_Store
+Thumbs.db
+
+# Agent / internal (must never appear)
+.agent/
+.claude/
+.kiro/
+competitors/