DX: add a dev:reset script that clears local storage

[1nonlypiece]

Summary

npm run dev:reset prints the URL (http://localhost:<port>/?dev-reset) that clears the app's localStorage. A Node script can't reach into a running browser's storage directly, so the actual clearing happens client-side: a new DevResetHandler (mounted in Providers.tsx, same Suspense-wrapped useSearchParams pattern as the existing DevRequestIdDisplay) watches for the ?dev-reset param, clears every key in the new DEV_RESET_LOCAL_STORAGE_KEYS registry (theme preference, display density, "what's new" seen-state, dev mode), then strips the param so a refresh doesn't re-clear.

Testing

• node scripts/dev-reset.mjs -- prints the expected URL
• node node_modules/vitest/vitest.mjs run ... tests/unit/dev/resetLocalStorage.test.ts -- 3/3 pass
• npm run test:unit:vitest -- 300 passing (was 297 on main), zero regressions
• npx eslint on all touched files -- clean
• npx tsc --noEmit -- no new errors in any touched file

Closes #1500