feat: persist emulator speed setting per core/game

[aaron30128840]

Feature Request

Currently there is no way to set a persistent speed multiplier for emulation. The only option is holding Space for fast-forward — which requires continuous input and is unavailable on mobile entirely.

Problems

1. No persistent speed setting — there is no way to configure a fixed speed multiplier (e.g. 2x) that stays active without user input.
2. Fast-forward requires holding Space — the current fast-forward is not a toggle but requires continuous key press, making it impractical for longer sessions.
3. Mobile inaccessible — Space has no touch equivalent, leaving mobile users with no speed control at all.

Use Case

Slow-paced games like Pokémon (GB/GBC/GBA) are a primary example where a persistent 2x–4x speed setting would significantly improve the experience. Having to hold Space for minutes at a time — or being unable to speed up at all on mobile — makes these games tedious to play.

Proposed Solution

1. Persistent speed multiplier — configurable per core or per game, stored in retroassembly.sqlite.
2. Space as toggle — make fast-forward a toggle instead of requiring continuous hold.
3. On-screen speed control — touch-friendly speed button/slider in the mobile UI overlay.

Environment

• RetroAssembly: latest (self-hosted via Docker)
• Affected: all platforms, especially mobile (iOS Safari, Chrome Android)
• Most impacted cores: GB, GBC, GBA (e.g. Pokémon series)