refactor: address review findings #51-54, #59

[silverbucket]

Summary

Five small, independent cleanups from the comprehensive review.

• App.svelte: dieColor / customDieColor derives are duplicates; else-branch is dead #54 — App.svelte: collapse dieColor / customDieColor derives into one. The else branch on the CSS-variable effect was dead code (the --accent* properties are never set when customDieColor is null in the first place).
• iOS PWA scroll-nudge re-runs on every account swap #59 — App.svelte: latch the iOS-PWA scroll-nudge so it only fires the first time initialSyncComplete flips to true. Account swaps re-flip it true → false → true, so each swap was triggering another (harmless but wasted) nudge.
• Dead code: setlistViewVersion / {#key} forced re-mount #51 — RollScreen.svelte + stores/app.svelte.js: drop the {#key store.setlistViewVersion} wrapper and the matching setlistViewVersion state. Svelte 5's reactivity already updates the keyed {#each} cleanly when generatedSetlist changes — no need to tear down and rebuild the whole result subtree on every roll. Audit notes:
  • SetlistSongCard's expanded state now persists across rolls when the same song happens to repeat (keyed by song.id). Reasonable UX.
  • .result-section's pop-in animation now only runs the first time the section mounts (i.e., the first roll after an empty state). The dice button's landed bounce + confetti still gives feedback on every subsequent roll.
• Drop or inline scopedKey now that accountSlot is the API #53 — accounts.js: make scopedKey module-private. accountSlot(address).key(base) is the public API. Tests rewritten to exercise the same behavior through accountSlot.
• Bloat: hex helpers in utils.js share validate→parse pattern #52 — utils.js: extract a parseHex(hex) → [r, g, b] helper that internalizes the validate-and-fallback pattern, drop the recursive fallback in each formatter, and add a toHexByte helper for darkenHex.

Closes #51, #52, #53, #54, #59 once merged.

Test plan

• npm run lint — clean
• npm test — 276/276 pass
• npm run build — succeeds
• npm run test:e2e — 136/136 pass