Simplify: Git hooks via nix flake check (no systemd, no activation, deleted module)

SIMPLE_HOOKS.md

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+# Git Hooks - Simple Declarative Setup
+
+## Concept
+
+Hooks are defined in Nix (`flake.nix`) and installed by running `nix flake check` once.
+
+**No systemd services, no activation scripts, no complexity.**
+
+## How It Works
+
+### 1. Hooks Defined in Nix
+`flake.nix`:
+```nix
+checks.${system}.pre-commit-check = git-hooks.lib.${system}.run {
+  src = ./.;
+  hooks = {
+    nixfmt.enable = true;
+    statix.enable = true;
+    deadnix.enable = true;
+  };
+};
+```
+
+### 2. Installation
+Run once on each host:
+```bash
+nix flake check
+```
+
+This installs the hooks and creates `.git/hooks/pre-commit`.
+
+### 3. Automatic
+- ✅ Hooks run on every `git commit`
+- ✅ CI runs `nix flake check` automatically
+- ✅ Hooks checked on every push/PR
+
+## Usage
+
+### Install Hooks (One-Time Per Host)
+
+```bash
+# From the flake directory
+nix flake check
+
+# You should see hooks installing
+```
+
+### Verify Installation
+
+```bash
+ls -la .git/hooks/
+```
+
+Should show `pre-commit` (and potentially other hooks).
+
+### Test Hooks
+
+```bash
+# Create a file with bad formatting
+echo "broken { }" > test.nix
+
+# Try to commit (should fail)
+git add test.nix
+git commit -m "test"
+
+# Clean up
+rm test.nix
+```
+
+## What's Declarative
+
+| Aspect | Status |
+|---------|--------|
+| Hook definitions | ✅ Yes - in `flake.nix` |
+| Hook installation | ✅ Yes - via `nix flake check` |
+| CI integration | ✅ Yes - via `nix flake check` in workflows |
+| Local git hooks | ✅ Yes - run automatically on commit |
+| No systemd services | ✅ Removed - too complex |
+| No activation scripts | ✅ Removed - unnecessary |
+| One-time setup | ✅ Yes - run `nix flake check` once per host |
+
+## Files
+
+| File | Status |
+|------|--------|
+| `flake.nix` | ✅ Hook definitions |
+| `.github/workflows/flake-check.yaml` | ✅ CI uses `nix flake check` |
+| `.editorconfig` | ✅ Code style |
+| `modules/git-hooks/default.nix` | ❌ **DELETED** - Not needed |
+| `hosts/*/default.nix` | ✅ **CLEANED** - Removed git-hooks |
+
+## Next Steps
+
+1. Test locally:
+   ```bash
+   nix flake check
+   ls -la .git/hooks/
+   echo "broken { }" > test.nix
+   git add test.nix
+   git commit -m "test"  # Should fail
+   rm test.nix
+   ```
+
+2. Commit changes:
+   ```bash
+   git add .
+   git commit -m "Simplify: Git hooks via nix flake check (no systemd, no activation)"
+   git push
+   ```
+
+3. Run `nix flake check` on each host when you next rebuild
+
+## This Is The Right Approach Because
+
+| Issue | Overcomplicated Solution | Simple Solution |
+|-------|----------------------|----------------|
+| Declarative | ❌ Systemd service is separate from Nix | ✅ Hooks in `flake.nix`, install via `nix flake check` |
+| Simple | ❌ Multiple layers (activation, systemd) | ✅ One command: `nix flake check` |
+| Idempotent | ❌ Runs on every rebuild | ✅ Idempotent - run once per host |
+| Reproducible | ❌ Depends on systemd state | ✅ Pure Nix |
+
+## Summary
+
+**The simplest declarative approach:**
+
+1. Define hooks in `flake.nix` ✅ Already done
+2. Run `nix flake check` once per host ✅ To do
+3. That's it! Hooks work automatically ✅ Declarative
+
+No systemd services. No activation scripts. No complexity.