feat(agents): role orchestrateur du contexte global expose et configurable par agent — isOrchestrator distinct des permissions MCP, DTO update_project_orchestrator (terminologie wire legacy conservee), refus idea_context_update explicite avec writer effectif + orientation idea_context_propose, surface AgentsPanel + adaptateurs frontend — #276 (QA verte: cargo fmt/check, tests cibles application/app-tauri/infrastructure/backend, npm typecheck, 69/69 tests frontend agents/adapters)

frontend/src/ports/index.ts

@@ -277,6 +277,11 @@ export interface AgentGateway {
     agentId: string,
     contactable: boolean,
   ): Promise<Agent>;
+  /** Selects the project's single writer of the global shared context. */
+  updateProjectOrchestrator(
+    projectId: string,
+    agentId: string,
+  ): Promise<{ orchestratorAgentId: string }>;
   /** Reads an agent's `.md` context by agent id. */
   readContext(projectId: string, agentId: string): Promise<string>;
   /** Overwrites an agent's `.md` context. */