visual(themes): add Banana, Lava, Beach, Xray themes, scrollable theme picker, remove developer theme

[aaf2tbz]

Summary

Adds four new app themes — Banana, Lava, Beach, Xray — reworked the theme picker from a dropdown into an in-place scrollable popover (now that there are 10 themes), and removes the developer theme. Renderer-only change; no backend, launch-path, or bottle behavior touched.

Changes

• Banana — soft creamy yellow surfaces, white text, saturated yellow buttons with dark text; seamless banana-slices.png background tile (offset-crossfade seamless + wrap-aware blur)
• Lava — crimson fire palette, red-hued game cards, truly black smoldering buttons and search/inputs with ember hover/focus rings; lava-cracks.png glowing-cracks tile
• Beach — tropical sand tones, white text, sandy buttons, clean blue underglow on cards and hovers; full-bleed beach-sand.png dune background (background-size: cover, no tile seams)
• Xray — near-black base with a soft phosphor-green wireframe grid, orange accent highlights, green-on-black bordered buttons (retrofuturist poster look)
• Each new theme has its own nav-icon set (library/sharp/logs/refresh/steam) via themeNavIcons
• Theme picker — now a scrollable popover: capped height, scroll-snap, themed thin scrollbar, header row, and auto-scrolls the active theme into view on open
• Developer theme removed (theme only — the developerMode settings feature is untouched); the two main-process spots that passed theme: "developer" to windows now fall back to "dark"

PR Readiness (MANDATORY)

• Compatibility verified with at least one real game (game + launch method noted below)
• No hardcoded paths, secrets, or absolute /Users/... paths introduced
• Config/rules TOML validated if configs/mtsp-rules.toml or DLL maps changed
• Version triple (CMakeLists.txt, Cargo.toml, package.json, package-lock.json) in sync if version bumped
• Bottle/runtime migration and launch behavior preserved (rollback plan noted if changed)
• Docs / compatibility matrix updated for user-facing changes
• Regression test added for each bug fix

Local toolchain (run before push)

• cargo fmt --all -- --check passes (Rust) — N/A, no Rust changes
• cargo clippy --all-targets -- -D warnings passes (Rust) — N/A
• cargo build --release passes (Rust backend) — passes (unchanged, verified locally)
• cargo test passes (Rust) — N/A, no Rust changes
• C++ compiles if changed — N/A, no C++ changes
• clang-format --dry-run --Werror passes — N/A
• ctest --test-dir build-native passes if tests changed — N/A
• TypeScript compiles if changed: cd app && npx tsc --noEmit — passes
• Biome + Prettier pass if TS/JS changed — biome ci src/ passes (3 pre-existing warnings on main pattern) and prettier --check passes
• Shell scripts lint if changed — N/A
• tools/ci/validate-rules-toml.py passes — N/A
• python3 tools/ci/verify-dmg-workflow.py passes — N/A
• Tested with at least one game — N/A: renderer-only theming; verified in Electron preview (npm run preview:dev, backend built with cargo build --release); all 10 themes cycled via the picker
• No hardcoded paths, secrets, or absolute /Users/... paths
• No new files should be added to the repo root; place them under app/, tools/, tests/, etc. — new assets under app/src/renderer/assets/

Test notes

Built the Rust backend (cargo build --release) and launched the Electron app via npm run preview:dev. Cycled through all 10 themes with the new scrollable picker: verified token application, per-theme nav icons, button treatments per theme spec (yellow/black/sandy/wireframe), background textures (no seams/kaleidoscope artifacts), picker scroll + snap + active-theme-into-view, and localStorage persistence across relaunch. No game launch testing — this PR does not touch launch, bottle, runtime, or routing code.

Risk

Low. Renderer CSS/TS only plus a two-line theme-fallback change in main/index.ts. Worst case is a visual regression in one theme; rollback is reverting this commit. The removed developer theme falls back to dark automatically for any stale saved preference.