Feat v0.8.2 capability negotiation (#69)

Extensions declare environment requirements via capabilities.required and
capabilities.optional in their manifest. The kernel validates at install
time — required capabilities reject with HTTP 422 and rollback, optional
capabilities log a warning. Runtime query via settings.has_capability().
Admin endpoint GET /api/v1/admin/capabilities re-probes live.

Detected capabilities: postgres, pgvector, object_storage, s3, workspace.

18 new tests, all passing with -race.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/sandbox/settings_module_test.go

@@ -0,0 +1,75 @@
+package sandbox
+
+import (
+	"context"
+	"testing"
+
+	"go.starlark.net/starlark"
+
+	"armature/store"
+)
+
+func execWithSettings(t *testing.T, caps map[string]bool, script string) (*Result, error) {
+	t.Helper()
+	ctx := context.Background()
+	mod := BuildSettingsModule(ctx, store.Stores{}, "", "", "", caps)
+	sb := New(DefaultConfig())
+	return sb.Exec(ctx, "test.star", script, map[string]starlark.Value{
+		"settings": mod,
+	})
+}
+
+func TestHasCapability_True(t *testing.T) {
+	caps := map[string]bool{"postgres": true, "pgvector": true}
+	result, err := execWithSettings(t, caps, `
+result = settings.has_capability("pgvector")
+`)
+	if err != nil {
+		t.Fatalf("exec error: %v", err)
+	}
+	v := result.Globals["result"]
+	if v != starlark.True {
+		t.Errorf("has_capability('pgvector') = %v, want True", v)
+	}
+}
+
+func TestHasCapability_False(t *testing.T) {
+	caps := map[string]bool{"postgres": true, "pgvector": false}
+	result, err := execWithSettings(t, caps, `
+result = settings.has_capability("pgvector")
+`)
+	if err != nil {
+		t.Fatalf("exec error: %v", err)
+	}
+	v := result.Globals["result"]
+	if v != starlark.False {
+		t.Errorf("has_capability('pgvector') = %v, want False", v)
+	}
+}
+
+func TestHasCapability_UnknownCap(t *testing.T) {
+	caps := map[string]bool{"postgres": true}
+	result, err := execWithSettings(t, caps, `
+result = settings.has_capability("gpu")
+`)
+	if err != nil {
+		t.Fatalf("exec error: %v", err)
+	}
+	v := result.Globals["result"]
+	if v != starlark.False {
+		t.Errorf("has_capability('gpu') = %v, want False", v)
+	}
+}
+
+func TestHasCapability_NilCaps(t *testing.T) {
+	result, err := execWithSettings(t, nil, `
+result = settings.has_capability("postgres")
+`)
+	if err != nil {
+		t.Fatalf("exec error: %v", err)
+	}
+	v := result.Globals["result"]
+	if v != starlark.False {
+		t.Errorf("has_capability with nil caps = %v, want False", v)
+	}
+}