feat: aiosendspin protocol compliance

[chrisuthe]

Summary

• Send static_delay_ms in client/state messages — Server uses this for GroupSync calibration to compensate for device audio output latency across the group
• Clear artwork on empty binary payload — Server sends empty artwork message (type 8-11, 0-byte data) to signal "no artwork"; previously showed stale artwork
• Advertise 32-bit PCM in supported formats — Remove 24-bit cap so WASAPI devices report native 32-bit depth; SDK's PcmDecoder and NAudio already handle it
• SDK version bumped to 7.1.0 (minor, backward-compatible additions)
• App version bumped to 1.12.0

Matches protocol gaps identified in SendspinDroid PR #44 audit against aiosendspin server source.

Test plan

• Connect to a server, verify static_delay_ms appears in client/state JSON in server logs
• Play a track with artwork, switch to one without — album art should clear to placeholder
• Check client hello logs for 32-bit bit depth in supported_formats (device-dependent)
• Verify build succeeds with no new errors

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