Replace placeholder Jest test with baseline utility coverage

[alx-so]

Problem

The test suite exists but currently has no implemented coverage. The only test is a placeholder, so yarn test can pass without exercising the library behavior.

Start with pure utility and hook-adjacent logic because these tests are fast, deterministic, and do not require a rendered React Native environment.

Impact

Baseline unit coverage gives bug-fix PRs an immediate regression signal before component-level tests are expanded.

Code references

• src/__tests__/index.test.tsx#L1: placeholder test should be replaced or removed once real tests exist.
• src/common/composePartialTextNode.tsx#L3-L25: match-tag rendering and tag stripping helpers.
• src/components/Input/utils.ts#L5-L30: input value normalization and tag composition helpers.
• src/components/Select/utils.ts#L5-L31: multi-value selection helpers.
• src/hooks/useSearch.ts#L13-L59: search result mapping and match highlighting behavior.

Acceptance criteria

• Placeholder-only test file is replaced by meaningful tests or removed after real tests exist.
• Tests cover removeTags, composeValue, composeTags, removeItemFromMultipleValue, and isItemSelected.
• Tests cover search matching and highlighted-label output for a stable item list.
• Tests are deterministic and do not depend on wall-clock generated IDs unless time is mocked.
• Tests run through the existing Jest command without starting an app server.