fix(raycast): display zero relevance scores

[vivekvar-dl]

Summary

Search accepts a zero relevance threshold, so a result can legitimately have score: 0. The Raycast extension used truthiness checks and hid that value in both the result list and detail view.

Check for undefined instead so zero renders as 0% while an omitted score remains hidden.

Verification

• bunx biome check src/search-memories.tsx
• npm run build in apps/raycast-extension
• npx tsc --noEmit -p tsconfig.json
• git diff --check

Repository-wide checks

• bun run format-lint — blocked by existing repository diagnostics (3 errors and 104 warnings, including Biome schema-version mismatches); no fixes were applied
• bun run check-types — blocked in the unchanged packages/ui/components/shadcn-io/dropzone.tsx because react-dropzone is not declared/installed
• bun run build — all 7 build tasks completed successfully; the root command then failed in postbuild because the Sentry upload requires a maintainer auth token

Additional regression coverage

• bun test src/relevance-score.test.ts (3 passed)
• bunx biome check apps/raycast-extension/src/search-memories.tsx apps/raycast-extension/src/relevance-score.ts apps/raycast-extension/src/relevance-score.test.ts
• Raycast extension build and TypeScript check both pass after extracting the shared formatter

Screenshots

Not included: the development command reaches the Supermemory API-key setup screen, and reproducing an exact zero-score response requires authenticated live data. The zero-score list/detail behavior is covered by the focused regression test instead.