feat(builder): log build failure output as separate lines

Log each line of build failure output as a separate structured log entry
at WARN level, making output readable and queryable in Loki/Grafana.
Add repo and rev fields to all build-related log entries. Add
truncateOutputLines helper that returns a []string for per-line logging.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cmd/homelab-deploy/main.go

@@ -17,7 +17,7 @@ import (
 	"github.com/urfave/cli/v3"
 )
 
-const version = "0.2.2"
+const version = "0.2.3"
 
 func main() {
 	app := &cli.Command{