Feat v0.10.0 panel manifest lifecycle

Panels are a new kernel rendering tier between surfaces and block
renderers, enabling composable companion views (e.g. notes panel
inside chat). This version ships the plumbing layer:

- Manifest validation for panels field (provider map + consumer array)
- Soft-dep warning at install time for unresolved panel consumers
- PanelMeta struct + resolvePanels() resolves consumers at surface load
- window.__PANELS__ injected into base template
- sw.panels SDK module (open/close/toggle/isOpen/isAvailable/list/active)
- Lazy JS loading pipeline with module caching
- 10 new tests (6 validation + 4 resolve)

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

server/handlers/package_validate_test.go

@@ -349,3 +349,100 @@ func TestValidateManifest_AutoSynthesizeSurfaces(t *testing.T) {
 		t.Errorf("expected layout 'editor', got %q", s["layout"])
 	}
 }
+
+// ── Panels validation (v0.10.0) ─────────────────────────────
+
+func TestValidateManifest_PanelsProviderValid(t *testing.T) {
+	m := map[string]any{
+		"id":    "my-notes",
+		"title": "Notes",
+		"panels": map[string]any{
+			"reference": map[string]any{
+				"entry": "js/panels/reference.js",
+				"title": "Notes Reference",
+				"icon":  "📝",
+			},
+		},
+	}
+	info, err := ValidateManifest(m)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !info.HasPanels {
+		t.Error("expected HasPanels to be true")
+	}
+}
+
+func TestValidateManifest_PanelsProviderMissingEntry(t *testing.T) {
+	m := map[string]any{
+		"id":    "my-notes",
+		"title": "Notes",
+		"panels": map[string]any{
+			"reference": map[string]any{
+				"title": "Notes Reference",
+			},
+		},
+	}
+	_, err := ValidateManifest(m)
+	if err == nil {
+		t.Fatal("expected error for panel missing entry")
+	}
+}
+
+func TestValidateManifest_PanelsProviderMissingTitle(t *testing.T) {
+	m := map[string]any{
+		"id":    "my-notes",
+		"title": "Notes",
+		"panels": map[string]any{
+			"reference": map[string]any{
+				"entry": "js/panels/reference.js",
+			},
+		},
+	}
+	_, err := ValidateManifest(m)
+	if err == nil {
+		t.Fatal("expected error for panel missing title")
+	}
+}
+
+func TestValidateManifest_PanelsConsumerValid(t *testing.T) {
+	m := map[string]any{
+		"id":    "my-chat",
+		"title": "Chat",
+		"panels": []any{"notes.reference", "notes.graph"},
+	}
+	info, err := ValidateManifest(m)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if len(info.PanelConsumers) != 2 {
+		t.Fatalf("expected 2 panel consumers, got %d", len(info.PanelConsumers))
+	}
+	if info.PanelConsumers[0] != "notes.reference" {
+		t.Errorf("expected 'notes.reference', got %q", info.PanelConsumers[0])
+	}
+}
+
+func TestValidateManifest_PanelsConsumerInvalidFormat(t *testing.T) {
+	m := map[string]any{
+		"id":    "my-chat",
+		"title": "Chat",
+		"panels": []any{"notes-no-dot"},
+	}
+	_, err := ValidateManifest(m)
+	if err == nil {
+		t.Fatal("expected error for consumer panel without dot separator")
+	}
+}
+
+func TestValidateManifest_PanelsInvalidType(t *testing.T) {
+	m := map[string]any{
+		"id":     "my-pkg",
+		"title":  "My Package",
+		"panels": "invalid-string",
+	}
+	_, err := ValidateManifest(m)
+	if err == nil {
+		t.Fatal("expected error for panels as string (neither map nor array)")
+	}
+}