launcher: additional UI functionality (scanlines card, host-shortcut chord labels, TurboToggle)

[kerokline]

Supersedes #42 (same scanlines commits, plus one more launcher uplift merged on top). Two small PSX launcher additions that touch the same settings/controller surfaces:

1. Scanlines toggle + strength on the Display card

Adds a Scanlines checkbox and a strength slider to the Display settings for consoles that advertise has_scanlines (set in the PSX profile). The strength row appears only once scanlines are on.

ABI (additive):

• RecompLauncherCSettings.scanlines and .scanline_strength_pct appended at the end of the struct.
• RecompLauncherCGameInfo.has_scanlines appended at the end of the struct.
• #define RECOMP_LAUNCHER_HAS_SCANLINES 1 so hosts can #ifdef for source compatibility.

Mirrors the existing screen_kind wiring throughout (model capability, seed/apply, UI row). No behavioural change for any console that leaves has_scanlines at 0.

The scanline effect itself lives in the runtime (companion psxrecomp PR — the present-path shader). Without that runtime support the control is inert but harmless; the two are meant to land together.

2. Host Shortcuts: label the implicit Select chord; TurboToggle hotkey

The PSX runtime only matches a host shortcut bound to one button or one trigger direction while Select is also held (hotkey_pad_binding_down). The capture UI already swallows a lone Select for that reason, but the resulting label showed just righttrigger+, so a player who bound R2 pressed R2 alone and saw nothing happen.

• On the PSX profile, single-button / single-axis bindings now render as select + righttrigger+ in both host-shortcut tables, with a one-line hint under the table (capture two buttons together for a chord without Select). Explicit two-button chords are unchanged.
• Surfaces the runtime's new [KeyMap] TurboToggle (press-to-latch fast-forward, default F9): LNG_HK_TURBO_TOGGLE, key/default/label tables, and the PSX hotkeys_mask.

Companion runtime PR: RetroPortingToolKit/psxrecomp#318 (feat/fast-forward-toggle): adds the toggle itself and the fourth host-shortcut row, [hotkeys] fast_forward_toggle_pad. Without it the launcher change is harmless: the extra hotkey row is inert and the label prefix is purely cosmetic.

3. Backspace clears a host shortcut / hotkey while listening

There was no way to remove a binding: capture commits any key or button, Esc keeps the old value, Reset restores every default at once. Backspace during a host-shortcut capture now stores 0 (unbound) for the keyboard or controller column; on the Hotkeys list it writes the literal None, which the runtime honours as an explicit unbind via RetroPortingToolKit/psxrecomp#319 (merged #318 does not need it for the toggle itself).

4. Controller column hidden when Player 1 has no connected gamepad

The PSX runtime evaluates controller host shortcuts against Player 1's pad handle only, so with the seat on Keyboard / None or the pad unplugged, nothing bound there can fire. Both tables now drop the Controller column in that state and say why. Other profiles are unchanged.

Verified in a BoF3 build: the host-shortcut table shows select + lefttrigger+ for a seeded axis binding, and stored chords still read select + r3.

🤖 Generated with Claude Code

[kerokline]

fixed merge issues, bumped to match master.

[mstan]

Rebased onto master (b688ca7) as one squashed commit. The merge from master had put scanlines/scanline_strength_pct and has_scanlines in the middle of RecompLauncherCSettings/RecompLauncherCGameInfo; they're now at the struct ends (append-only ABI). LNG_HK_TURBO_TOGGLE comes after master's LNG_HK_OPEN_LAUNCHER. ctest: SDL3 25/25.

🤖 Generated with Claude Code