Add navbar terminate action for active cloud sessions

[zortos293]

Description

This PR implements issue #316, allowing users to forcibly terminate an active cloud session from the navbar while the app is idle. Previously, users could only resume sessions but had no way to close a stuck session without connecting to it.

Main changes:

• Shared stop helper (src/renderer/src/App.tsx): Extracted stopSessionByTarget to centralize session stop request assembly and auth token handling; reused by both the existing in-stream stop flow and the new navbar terminate flow.

• Navbar terminate handler (src/renderer/src/App.tsx): Added handleTerminateNavbarSession with user confirmation via window.confirm, guarded against concurrent resume/terminate/play actions, loading state (isTerminatingNavbarSession), error handling, and automatic refresh of the active session list after completion.

• Race prevention (src/renderer/src/App.tsx): Introduced navbarSessionActionInFlightRef to track "resume" or "terminate" operations in-flight; guards in handleResumeFromNavbar, handleTerminateNavbarSession, and handlePlayGame prevent overlapping actions.

• ActiveSessionInfo extension (src/shared/gfn.ts, src/main/gfn/cloudmatch.ts): Added streamingBaseUrl field to the active session payload so terminate requests can include the correct base URL without requiring new backend plumbing.

• Navbar UI (src/renderer/src/components/Navbar.tsx): Replaced the standalone resume button with a flex navbar-session-actions container containing paired Resume (green) and Terminate (red) buttons; both show loading spinners during their respective operations and are disabled during conflicting actions.

• Styling (src/renderer/src/styles.css): Added .navbar-session-terminate and .navbar-session-actions variants with error-tone gradients on hover/focus; responsive rules hide the Terminate label on narrower screens; controller-mode size adjustments applied.