feat(coding-agent): add session naming via /name command and extension API

- Add SessionInfoEntry type for session metadata
- Add /name <name> command to set session display name
- Add pi.setSessionName() and pi.getSessionName() extension API
- Session selector shows name (in warning color) instead of first message when set
- Session name included in fuzzy search
- /session command displays name when set

closes #650

packages/coding-agent/src/core/extensions/loader.ts

@@ -86,6 +86,8 @@ export function createExtensionRuntime(): ExtensionRuntime {
 		sendMessage: notInitialized,
 		sendUserMessage: notInitialized,
 		appendEntry: notInitialized,
+		setSessionName: notInitialized,
+		getSessionName: notInitialized,
 		getActiveTools: notInitialized,
 		getAllTools: notInitialized,
 		setActiveTools: notInitialized,
@@ -169,6 +171,14 @@ function createExtensionAPI(
 			runtime.appendEntry(customType, data);
 		},
 
+		setSessionName(name: string): void {
+			runtime.setSessionName(name);
+		},
+
+		getSessionName(): string | undefined {
+			return runtime.getSessionName();
+		},
+
 		exec(command: string, args: string[], options?: ExecOptions) {
 			return execCommand(command, args, options?.cwd ?? cwd, options);
 		},