Don't require lefthook to be installed

Set assert_lefthook_installed to false so the hooks gracefully skip
if lefthook is not installed on the system.

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

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

Author: pcarleton

lefthook.yml

@@ -1,7 +1,7 @@
 # lefthook.yml
 # Configuration reference: https://lefthook.dev/configuration/
 
-assert_lefthook_installed: true
+assert_lefthook_installed: false
 
 output:
   - meta # Print lefthook version