test: Add Vitest unit tests for location-detector and country-flags helpers #232

The geo utility module (src/lib/geo/location-detector.ts and src/lib/geo/country-flags.ts) maps user location strings to normalized country slugs and ISO flag codes using regex keyword matching, but currently lacks unit test coverage.

Motivation

Testing country normalization ensures regex boundary matching does not fail or produce false positives for similar words.

Tasks

• Create src/lib/geo/tests/location-detector.test.ts.
• Test exact match locations (e.g., 'Egypt' -> 'egypt', 'Germany' -> 'germany', 'Tokyo, Japan' -> 'japan').
• Test word boundary handling to ensure substrings don't falsely match (e.g., words containing country substrings).
• Test edge cases: null, empty string, special characters, whitespace.
• Test getCountryCode in country-flags.ts for valid and unknown slugs.
• Run pnpm test and verify all tests pass.