Adds knip (pnpm knip, knip.ts covering src, scripts, perf and e2e) and runs it in the CI frontend job. Removes what it reported: the unused codemirror and @types/dompurify dependencies, exports and test hooks used nowhere (AppLogo, Tooltip, barrel re-exports, duplicate default exports of lazily loaded settings pages), the unused iterateAll helper, and the zh entry for a deleted notification. rustfmt (used by lint-staged) is ignored as a toolchain binary.
Co-authored-by: jaw52 <[email protected]>