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/api/variables.go

@@ -218,12 +218,14 @@ func handleUpdateVariables(c *gin.Context) {
 			`SELECT id, project_id, name, COALESCE(image, ''), COALESCE(command, ''),
 			        COALESCE(replicas, 1), COALESCE(port, 0), COALESCE(domain, ''),
 			        COALESCE(healthcheck_path, ''), COALESCE(restart_policy, 'unless-stopped'),
-			        COALESCE(cpu, ''), COALESCE(memory, '')
+			        COALESCE(cpu, ''), COALESCE(memory, ''),
+			        COALESCE(builder, 'auto'), COALESCE(cpu_reserve, ''), COALESCE(memory_reserve, '')
 			 FROM services WHERE id = $1`,
 			serviceID,
 		).Scan(&svc.ID, &svc.ProjectID, &svc.Name, &svc.Image, &svc.Command,
 			&svc.Replicas, &svc.Port, &svc.Domain, &svc.HealthCheckPath,
-			&svc.RestartPolicy, &svc.CPU, &svc.Memory)
+			&svc.RestartPolicy, &svc.CPU, &svc.Memory,
+			&svc.Builder, &svc.CPUReserve, &svc.MemoryReserve)
 		resp["redeploy_queued"] = svcErr == nil && enqueueServiceRedeploy(c, db.(*database.DB), svc)
 	}
 	c.JSON(http.StatusOK, resp)