v1.0.0

• Initial stable release.
• DbFlagProvider and CachedFlagProvider now implement
  Rasuvaeff\Yii3FeatureFlags\WritableFlagProvider (new in core 1.0.0):
  • save(Flag) — upsert keyed by flag name.
  • remove(string) — idempotent delete.
  • CachedFlagProvider is write-through: after delegating to a writable inner
    provider it clears its cache; on a read-only inner it is a silent no-op.
• FlagRowMapper::encodeEnvironments() (new public static method) is the
  inverse of extractEnvironments() and is used by DbFlagProvider::save().
  The two are round-trip compatible.
• DbFlagProvider::toRow() normalises salt to '' when it equals the flag
  name to preserve the emptySaltFallsBackToName invariant on read-back.
• config/di.php now binds WritableFlagProvider::class to the same instance
  as FlagProvider::class via Yiisoft\Definitions\Reference. One key, one
  vendor — no Duplicate key conflict with the core.
• Requires rasuvaeff/yii3-feature-flags ^1.0 and adds yiisoft/definitions ^3.0.
• FlagRowMapper now wraps \InvalidArgumentException from core (both
  InvalidFlagNameException for name and plain InvalidArgumentException
  for rollout range) into InvalidFlagRowException.