Connection manager in its own native window, modal to main

Single window centered over the main app. Electrobun has no native
modality, so it's approximated: bun bounces the main window's focus back
to the manager, the main webview shows a click-swallowing overlay, and
main-targeted menu/keyboard actions are dropped while open. Editor
windows stay fully usable. Connect/open-stack execute in the main
window via the existing connect: action channel; store edits push a
connectionsChanged refresh. Trigger moved from the panel dropdown to a
tab-bar button.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/shared/rpc.ts

@@ -140,6 +140,13 @@ export type AppRPC = {
 			/** Editor windows only — handled by that window's own rpc closure. */
 			editorSave: { params: { content: string }; response: Result };
 			editorClose: { params: Record<string, never>; response: Result };
+			// connection-manager window
+			/** Main window: open (or focus) the single connection-manager window. */
+			openConnectionManager: { params: Record<string, never>; response: Result };
+			/** Manager window only: connect/open-stack run in the MAIN window. */
+			managerConnect: { params: { id: string }; response: Result };
+			managerOpenStack: { params: { id: string }; response: Result };
+			managerClose: { params: Record<string, never>; response: Result };
 		};
 		messages: {
 			/** Editor → bun draft mirror; safety net for the non-cancellable native close. */
@@ -158,6 +165,10 @@ export type AppRPC = {
 			pathRefresh: { sessionId: string; dir: string };
 			/** bun → one editor: run the in-window close flow (dirty prompt). */
 			editorCloseRequest: Record<string, never>;
+			/** bun → main: the modal connection manager opened/closed. */
+			managerState: { open: boolean };
+			/** bun → main: the manager window changed the connection store. */
+			connectionsChanged: Record<string, never>;
 		};
 	};
 };