feat: Add presence heartbeat for Matrix online status

- matrix-gateway: POST /internal/matrix/presence/online endpoint
- usePresenceHeartbeat hook with activity tracking
- Auto away after 5 min inactivity
- Offline on page close/visibility change
- Integrated in MatrixChatRoom component

backend/domain/pdp/policy.model.ts

@@ -0,0 +1,38 @@
+/**
+ * PDP Policy Model
+ * Based on: pdp_access.md, core-services-mvp.md
+ */
+
+export type Decision = 'allow' | 'deny' | 'require-elevation';
+
+export type PolicyId = 
+  | 'policy.dao.create'
+  | 'policy.vendor.register'
+  | 'policy.platform.create'
+  | 'policy.federation.join'
+  | 'policy.federation.leave'
+  | 'policy.federation.create-superdao'
+  | 'policy.federation.dissolve'
+  | 'policy.agent.run';
+
+export interface PdpContext {
+  userId?: string;
+  daoId?: string;
+  daoLevel?: 'A1' | 'A2' | 'A3' | 'A4';
+  // Additional context: roles, balances, staking, etc.
+  [key: string]: unknown;
+}
+
+export interface PdpRequest {
+  policyId: PolicyId;
+  resource: Record<string, unknown>;
+  context: PdpContext;
+}
+
+export interface PdpResponse {
+  decision: Decision;
+  reason?: string;
+  details?: Record<string, unknown>;
+}
+
+