feat(services): builder selection, resource reservations, static builder (C3)

services.builder picks the build strategy per service: auto detects from
repo contents (Dockerfile → railpack → nixpacks), explicit overrides force
a builder, and static builds assets in a node stage then serves them from
an nginx image (static_build_cmd/static_dir, port 80 default).

- cpu_reserve/memory_reserve → Docker CPU shares + MemoryReservation;
  cpu/memory stay hard caps (NanoCPUs/Memory). Empty string clears.
- app_settings.default_cpu/default_memory override service-create
  fallbacks; capacity_policy=block fails deploys whose requested memory
  exceeds node capacity (default warn logs via slog).
- Resource specs are validated — "512mb" fails instead of silently
  dropping the limit.
- Fixes: deployments.go hardcoded nixpacks (auto-detect was dead code);
  DockerfileBuilder passed the Dockerfile *path* as build-context content;
  BuildImage never drained the daemon stream so builds could abort and
  errors went unseen — stream is now consumed and errorDetail surfaced.
- CLI: --builder/--cpu-reserve/--memory-reserve/--static-cmd/--static-dir
  on create+update; MCP args on services create/update; UI Build &
  Resources card; OpenAPI + llms.txt + CLI.md.

Verified live: static build of a real repo → nginx image → deployed;
reserves reach HostConfig (shares=256, MemoryReservation=128Mi);
validation rejects bad specs; builder persists + clears.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/backend/internal/build/dockerfile.go

@@ -211,8 +211,12 @@ func (d *DockerfileBuilder) Build(ctx context.Context, req *types.BuildRequest)
 	// Build Docker image
 	imageName := fmt.Sprintf("%s:%s", req.ImageName, req.ImageTag)
 
-	// Create build context tar
-	buildCtx, err := createBuildContext(req.SourcePath, optimizedDockerfile)
+	// createBuildContext wants the Dockerfile contents, not its path.
+	dockerfileContent, err := os.ReadFile(optimizedDockerfile)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read Dockerfile: %w", err)
+	}
+	buildCtx, err := createBuildContext(req.SourcePath, string(dockerfileContent))
 	if err != nil {
 		return nil, fmt.Errorf("failed to create build context: %w", err)
 	}