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)

crates/backend/src/dto.rs

@@ -3132,6 +3132,27 @@ pub struct UpdateAgentContactableRequestDto {
     pub contactable: bool,
 }
 
+/// Request DTO for `update_project_orchestrator`.
+///
+/// The legacy `orchestrator` terminology is intentionally kept on the wire for
+/// compatibility; the product-facing role is the global project-context writer.
+#[derive(Debug, Clone, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct UpdateProjectOrchestratorRequestDto {
+    /// Id of the owning project.
+    pub project_id: String,
+    /// Existing project agent that becomes the single effective writer.
+    pub agent_id: String,
+}
+
+/// Response DTO for `update_project_orchestrator`.
+#[derive(Debug, Clone, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct UpdateProjectOrchestratorResponseDto {
+    /// Effective writer agent id after the update.
+    pub orchestrator_agent_id: String,
+}
+
 /// Response DTO for `change_agent_profile`: the mutated agent plus the freshly
 /// relaunched session when a live session was hot-swapped (absent otherwise).
 #[derive(Debug, Clone, Serialize)]