Add /diff and /template commands

- /diff command to compare config with backups
  - Shows added/removed/changed files
  - JSON-aware comparison for config files
  - List available backups
- /template command for session templates
  - Built-in templates: daily-standup, code-review, troubleshoot, deploy
  - Each template includes checklist, initial commands, prompt
  - Create custom templates interactively or non-interactively
- Updated shell completions with 21 aliases total
- Test suite now covers 29 tests

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

commands/diff.md

@@ -0,0 +1,34 @@
+---
+name: diff
+description: Compare configuration with backup
+aliases: [config-diff, compare]
+invokes: command:diff
+---
+
+# Diff Command
+
+Compare current configuration with a backup to see what changed.
+
+## Usage
+
+```
+/diff                       # Compare with latest backup
+/diff --backup <file>       # Compare with specific backup
+/diff --list                # List available backups
+/diff --json                # Output as JSON
+```
+
+## Implementation
+
+```bash
+python3 ~/.claude/automation/config-diff.py [options]
+```
+
+## Output
+
+Shows changes grouped by type:
+- **Added** - New files in current config
+- **Removed** - Files that existed in backup but not now
+- **Changed** - Modified files with details
+
+For JSON files, shows which keys were added/removed/changed.