FPS overlay during the session

[lippdev]

Idea

Show an optional FPS counter over the game while console mode is active, toggled from the session menu (Select + Y) and in Settings.

Notes for later

• Source of the number: RTSS is already integrated for the FPS limit (Engine.Rtss), and its shared memory (RTSSSharedMemoryV2) exposes per-app frame time, so it's the natural first source. Without RTSS, options are PresentMon / ETW (DXGI present events; may need admin) or leaving the overlay unavailable, like the FPS limit row today.
• Drawing it: RTSS's own OSD already works over exclusive fullscreen; a Console Mode window (like the session toast) is simpler to style but, like the session menu, cannot cover exclusive-fullscreen games.
• UI: a toggle tile in the session menu, a corner position setting (top-left / top-right), maybe frame time and 1% low as extras.
• Controller: the toggle has to work with Xbox and PlayStation pads (see the HID reading from fix: session shortcuts (Select + Y, Start + Back) with PlayStation pads and with the Home option off #61 / feat: session menu with PlayStation pads, horizontal layout, start-of-session toast #64).

Not planned for a specific version yet.