feat(coding): add durable project identity core

shared/coding-project-contracts.ts

@@ -9,6 +9,10 @@ export interface CodingProjectSummary {
   lastOpenedAt: string;
 }
 
+export type ProjectIdentityChoice =
+  | { kind: 'create' }
+  | { kind: 'bind'; projectId: string };
+
 export interface CodingProjectAgent extends ConversationModelState {
   id: string;
   avatarId: string;
@@ -29,6 +33,7 @@ export interface CodingProjectAgent extends ConversationModelState {
 export interface CodingProjectConfig {
   schemaVersion: 2;
   projectType: ProjectType;
+  projectId?: string;
   initialized: boolean;
   agents: CodingProjectAgent[];
   knowledgeDirectory: 'knowledge';