- Add OsVersionRange interface + Zod schema (platform, minVersion?, maxVersion?)
- Add regions[] and osVersions[] to FeatureFlagDoc, CreateFlagSchema, UpdateFlagSchema
- Add compareVersions() helper for dot-separated semver comparison
- Extend GET /flags/poll with ?region and ?osVersion query params
- Region targeting: flag only returned if client region is in flag's regions list
- OS version targeting: per-platform min/max version range filtering
- Add 10 new tests (schema validation, compareVersions edge cases)
- 634 tests passing, tsc clean