add pre-commit hook to auto-update zat hash

run `just setup` after cloning to install the hook.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[e-mail]>

justfile

···
 default:
     @just --list
 
+setup:
+    cp scripts/pre-commit .git/hooks/pre-commit
+    chmod +x .git/hooks/pre-commit
+
 build:
     zig build
 

scripts/pre-commit

···
+#!/bin/sh
+# auto-update zig dependencies pointing to /archive/main
+
+# update zat hash if it changed
+zig fetch --save "https://tangled.org/zzstoatzz.io/zat/archive/main" 2>/dev/null || true
+
+# stage the updated build.zig.zon if it changed
+git diff --quiet build.zig.zon || git add build.zig.zon