feat: default list_alerts to active alerts only

Change list_alerts (MCP tool) and alerts (CLI command) to show only
active (non-silenced, non-inhibited) alerts by default. Add state=all
option and --all CLI flag to show all alerts when needed.

- MCP: list_alerts with no state param now returns active alerts only
- MCP: list_alerts with state=all returns all alerts (previous default)
- CLI: alerts command defaults to active, --all shows everything
- Add tests for new default behavior and state=all option
- Update README with new CLI examples
- Bump version to 0.3.0
- Clarify version bumping rules in CLAUDE.md

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

cmd/nixos-options/main.go

@@ -19,7 +19,7 @@ import (
 
 const (
 	defaultDatabase = "sqlite://nixos-options.db"
-	version         = "0.2.1"
+	version         = "0.3.0"
 )
 
 func main() {