test: cover non-object preference payload edge cases

[YRWoods]

Summary

Two focused regression tests for normalizeSearchPreferences edge cases that were not covered.

Problem

Fixes #11 — requested one untested preference edge case.

Approach

• Non-object payloads (null, string, number, boolean, array) → full defaults, no throw
• Unknown keys must not appear on the normalized object
• No production code change

How I tested

• Commented uncovered behavior on test: cover an untested search preference edge case #11 first
• node --test tests/*.test.js — 130 pass

Checklist

• One behavior only
• node:test + node:assert/strict
• Fixes test: cover an untested search preference edge case #11

[TuYv]

Thanks for adding regression coverage and for documenting the uncovered case on #11 first. The non-object payload test is on target and the full suite passes locally.

Please keep this PR to the one focused behavior requested by #11. It currently adds a second, independently named behavior for unknown-key stripping. Please remove that second test from this PR, or move it to a separate follow-up issue/PR, so this change remains limited to non-object preference payloads.

[YRWoods]

Addressed review: removed the second unknown-key stripping test. This PR is only the non-object payload coverage for #11.

[YRWoods]

Ready for re-review: dropped the second unknown-key test; PR is only non-object preference payloads for #11.

[YRWoods]

Re-review ready: second unknown-key stripping test removed in f644641. Diff is only the non-object preference payload test for #11.

[YRWoods]

Withdrawing.