feat: add ClaudeKit configuration

Add agent definitions, slash commands, hooks, and settings for
Claude Code project tooling.

.claude/commands/checkpoint/create.md

@@ -0,0 +1,31 @@
+---
+description: Create a git stash checkpoint with optional description
+category: workflow
+allowed-tools: Bash(git stash:*), Bash(git add:*), Bash(git status:*)
+argument-hint: "[optional description]"
+---
+
+## Create a checkpoint
+
+Create a git stash checkpoint to save your current working state.
+
+## Current status
+!`git status --short`
+
+## Task
+
+Create a git stash checkpoint while keeping all current changes in the working directory. Steps:
+
+1. If no description provided in $ARGUMENTS, use current timestamp as "YYYY-MM-DD HH:MM:SS"
+2. Create a stash object without modifying the working directory:
+   - First add all files temporarily: `git add -A`
+   - Create the stash object: `git stash create "claude-checkpoint: $ARGUMENTS"`
+   - This returns a commit SHA that we need to capture
+3. Store the stash object in the stash list:
+   - `git stash store -m "claude-checkpoint: $ARGUMENTS" <SHA>`
+4. Reset the index to unstage files: `git reset`
+5. Confirm the checkpoint was created and show what was saved
+
+Note: Using `git stash create` + `git stash store` creates a checkpoint without touching your working directory.
+
+Example: If user runs `/checkpoint before major refactor`, it creates a stash checkpoint while leaving all your files exactly as they are.