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/resources_test.go

@@ -0,0 +1,48 @@
+package api
+
+import "testing"
+
+func TestParseCPUReserveShares(t *testing.T) {
+	cases := map[string]int64{
+		"":      0,
+		"0":     0,
+		"-1":    0,
+		"abc":   0,
+		"0.25":  256,
+		"1":     1024,
+		"2.5":   2560,
+		" 0.5 ": 512,
+	}
+	for in, want := range cases {
+		if got := parseCPUReserveShares(in); got != want {
+			t.Errorf("parseCPUReserveShares(%q) = %d, want %d", in, got, want)
+		}
+	}
+}
+
+func TestValidateResourceSpecs(t *testing.T) {
+	if err := validateCPUSpec(""); err != nil {
+		t.Error("empty cpu should pass")
+	}
+	if err := validateCPUSpec("0.5"); err != nil {
+		t.Error("0.5 should be valid cpu")
+	}
+	if err := validateCPUSpec("512mb"); err == nil {
+		t.Error("512mb should fail cpu validation")
+	}
+	if err := validateMemorySpec(""); err != nil {
+		t.Error("empty memory should pass")
+	}
+	if err := validateMemorySpec("512Mi"); err != nil {
+		t.Error("512Mi should be valid memory")
+	}
+	if err := validateMemorySpec("1g"); err != nil {
+		t.Error("1g should be valid memory")
+	}
+	if err := validateMemorySpec("0.5"); err == nil {
+		t.Error("0.5 should fail memory validation (parses to <1 byte)")
+	}
+	if err := validateMemorySpec("lots"); err == nil {
+		t.Error("'lots' should fail memory validation")
+	}
+}