fix: bound in-memory cache size

[WilliamK112]

Summary

• cap the in-memory TTL cache at 500 entries
• evict the oldest inserted key before adding a new key at capacity
• preserve existing entries when an expired key is recomputed in place
• test the size bound, deterministic eviction, and recomputation behavior

Why

The cache used an unbounded Map, so distinct search and analytics keys could accumulate for the lifetime of the process. A simple FIFO cap keeps memory usage bounded while preserving the existing TTL and recomputation contracts.

Validation

• npx vitest run src/__tests__/cache.test.ts (10 passed)
• npm test (123 passed)
• npm run typecheck
• npm run build
• git diff --check

Closes #181

AI-assisted: Codex was used to help implement and validate this change; the final diff and tests were reviewed locally.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 0d61b1e9ba

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".