Add stream diagnostics to detect silent-but-"running" audio output

[Copilot]

The streamer can appear active (running: true, metadata updating) while sending only silence to hardware receivers — giving no observable signal that audio has stopped flowing. There was no way to distinguish real audio transmission from underrun-filler silence.

Changes

internal/streamer/streamer.go

• Added three sync/atomic.Int64 counters to Streamer: packetsSent, silencePackets, lastAudioPacketAt
• All three are reset on Start() and updated only after a successful conn.Write() — silence vs. real audio tracked via an isSilence flag
• Status struct extended with packets_sent, silence_packets, last_audio_packet_at; GET /api/status exposes them automatically

internal/web/static/index.html

• Added a 🔍 Stream-Diagnose panel, refreshed every 5 s alongside status, showing:
  • Total RTP packets sent / silence packet count
  • Silence ratio (%) — colour-coded 🟢 <10 % / 🟠 10–50 % / 🔴 >50 %
  • Timestamp of last real audio packet + human-readable staleness indicator

// GET /api/status — new fields
{
  "running": true,
  "station": "SWR3",
  "packets_sent": 4250,
  "silence_packets": 12,
  "last_audio_packet_at": 1744022548
}

internal/streamer/streamer_test.go

• Added TestCurrentStatusDiagnostics covering zero-init and counter accumulation

Original prompt

VOrschlag was soll ich machen zur KOntrolle dass die Audioasugabe auf dem nota142 Hardware nicht funktioniert obwohl es angezeigt wird DIe Stream Monitor Software auf meinem Rchner funktioniert einwandfrei

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