Feature Policies API + Invitations Policies (#375)

- Added Feature Policy API: a declarative system to enable/disable/modify default behavior in the SaaS kit
- Team invitation policies with pre-checks using the Feature Policy API: Invite Members dialog now shows loading, errors, and clear reasons when invitations are blocked
- Version bump to 2.16.0 and widespread dependency updates (Supabase, React types, react-i18next, etc.).
- Added comprehensive docs for the new policy system and orchestrators.
- Subscription cancellations now trigger immediate invoicing explicitly

packages/policies/src/registry.ts

@@ -0,0 +1,81 @@
+import { createRegistry } from '@kit/shared/registry';
+
+import type { FeaturePolicyDefinition } from './declarative';
+import type { PolicyContext } from './types';
+
+/**
+ * Simple policy registry interface
+ */
+export interface PolicyRegistry {
+  /** Register a single policy definition */
+  registerPolicy<
+    TContext extends PolicyContext = PolicyContext,
+    TConfig = unknown,
+  >(
+    definition: FeaturePolicyDefinition<TContext, TConfig>,
+  ): PolicyRegistry;
+
+  /** Get a policy definition by ID */
+  getPolicy<TContext extends PolicyContext = PolicyContext, TConfig = unknown>(
+    id: string,
+  ): Promise<FeaturePolicyDefinition<TContext, TConfig>>;
+
+  /** Check if a policy exists */
+  hasPolicy(id: string): boolean;
+
+  /** List all registered policy IDs */
+  listPolicies(): string[];
+}
+
+/**
+ * Creates a new policy registry instance
+ */
+export function createPolicyRegistry(): PolicyRegistry {
+  const baseRegistry = createRegistry<
+    FeaturePolicyDefinition<PolicyContext, unknown>,
+    string
+  >();
+
+  const policyIds = new Set<string>();
+
+  return {
+    registerPolicy<
+      TContext extends PolicyContext = PolicyContext,
+      TConfig = unknown,
+    >(definition: FeaturePolicyDefinition<TContext, TConfig>) {
+      // Check for duplicates
+      if (policyIds.has(definition.id)) {
+        throw new Error(
+          `Policy with ID "${definition.id}" is already registered`,
+        );
+      }
+
+      // Register the policy definition
+      baseRegistry.register(definition.id, () => definition);
+      policyIds.add(definition.id);
+
+      return this;
+    },
+
+    async getPolicy<
+      TContext extends PolicyContext = PolicyContext,
+      TConfig = unknown,
+    >(id: string) {
+      if (!policyIds.has(id)) {
+        throw new Error(`Policy with ID "${id}" is not registered`);
+      }
+
+      return baseRegistry.get(id) as Promise<
+        FeaturePolicyDefinition<TContext, TConfig>
+      >;
+    },
+
+    hasPolicy(id: string) {
+      return policyIds.has(id);
+    },
+
+    listPolicies() {
+      return Array.from(policyIds);
+    },
+  };
+}