Fix smart speakers not covered by 'Allow all media players' audit setting

[tvancott42]

Fixes #378

Summary

• Smart speakers (Google Home, Amazon Echo, Sonos, etc.) are now covered by the "Allow all media players on main network" audit setting
• Previously only Apple HomePods could be suppressed (via the Apple streaming setting) - all other smart speakers always generated a VLAN placement warning regardless of settings
• Updated settings gear metadata to point to media players setting instead of streaming devices

Test plan

• Existing tests pass (35/35 in DeviceAllowanceSettingsTests)
• New test: IsSmartSpeakerAllowed_AllowMediaPlayers_ReturnsTrue_ForAnyVendor
• Zero build warnings
• Deploy and verify: enable "Allow all media players", run audit, confirm smart speakers show as Informational (not Recommended)