feat: add CPU and memory resource limits per app

- Add cpu_limit (REAL) and memory_limit (INTEGER) columns to apps table
  via migration 007
- Add CPULimit and MemoryLimit fields to App model with full CRUD support
- Add resource limits fields to app edit form with human-friendly
  memory input (e.g. 256m, 1g, 512k)
- Pass CPU and memory limits to Docker container creation via
  NanoCPUs and Memory host config fields
- Extract Docker container creation helpers (buildEnvSlice, buildMounts,
  buildResources) for cleaner code
- Add formatMemoryBytes template function for display
- Add comprehensive tests for parsing, formatting, model persistence,
  and container options

internal/docker/resource_limits_test.go

@@ -0,0 +1,31 @@
+package docker //nolint:testpackage // tests unexported cpuLimitToNanoCPUs
+
+import (
+	"testing"
+)
+
+func TestCpuLimitToNanoCPUs(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name     string
+		cpuLimit float64
+		expected int64
+	}{
+		{"one core", 1.0, 1_000_000_000},
+		{"half core", 0.5, 500_000_000},
+		{"two cores", 2.0, 2_000_000_000},
+		{"quarter core", 0.25, 250_000_000},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			got := cpuLimitToNanoCPUs(tt.cpuLimit)
+			if got != tt.expected {
+				t.Errorf("cpuLimitToNanoCPUs(%v) = %d, want %d", tt.cpuLimit, got, tt.expected)
+			}
+		})
+	}
+}