feat: add ElevenLabs Scribe STT transcriber and Telegram SendVoice support (#1905)

* feat: add ElevenLabs Scribe STT transcriber and Telegram SendVoice support

Add ElevenLabsTranscriber as an alternative speech-to-text provider using
the ElevenLabs Scribe API (scribe_v1). This enables voice message
transcription for users who already have an ElevenLabs API key, without
requiring a separate Groq account.

Changes:
- Add ElevenLabsTranscriber implementing the Transcriber interface
- Update DetectTranscriber to check providers.elevenlabs.api_key first,
  falling back to Groq for backward compatibility
- Add ElevenLabs to ProvidersConfig
- Add "voice" media type for OGG files with "voice" in filename
- Add SendVoice support in Telegram channel for voice bubble messages
- Add comprehensive tests for ElevenLabs transcriber

Configuration:
  "providers": {
    "elevenlabs": {
      "api_key": "sk_your_key_here"
    }
  }

Closes #1503 (partial)

* fix: move voice-bubble detection into Telegram channel to avoid regression in other channels

Address review feedback: keep inferMediaType returning "audio" for all
OGG files. Voice-bubble detection (SendVoice vs SendAudio) is now done
inside the Telegram channel based on filename, so other channels that
map "audio" explicitly are unaffected.

* fix: align VoiceConfig struct tags to pass golines formatter

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix(agent): use ModelName in loop test added by upstream

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

pkg/agent/loop_test.go

@@ -1717,7 +1717,7 @@ func TestProcessMessage_PublishesReasoningContentToReasoningChannel(t *testing.T
 		Agents: config.AgentsConfig{
 			Defaults: config.AgentDefaults{
 				Workspace:         tmpDir,
-				Model:             "test-model",
+				ModelName:         "test-model",
 				MaxTokens:         4096,
 				MaxToolIterations: 10,
 			},