M4: voice pipeline (software-only telephony)

- AudioSocket server (asyncio TCP, Asterisk wire protocol) bridging calls
  into the same M2 agent used by chat
- Call session engine: greeting → energy-VAD utterance collection → STT →
  agent turn → TTS playback with barge-in (120ms of caller speech stops
  playback); inactivity + max-duration guards; unintelligible audio reaches
  the agent as '[nerazumljivo]' so the two-attempt rule stays in the prompt
- STTProvider (faster-whisper, lang hint 'sr', GPU/CPU via env) and
  TTSProvider (Azure Neural raw-8k PCM / ElevenLabs Flash) + test fakes
- Recording (mixed caller+agent WAV), transcripts, per-turn latency trace,
  metering via record_agent_call (§12)
- Internal dialplan API: /internal/calls/register (ring targets computed from
  working hours + ring settings §5.2), /answered (human outcome, no minutes),
  /hangup (abandoned → missed-call SMS §5.5); shared-token auth
- Asterisk config generator (pjsip.conf + extensions.conf from DB): worker
  endpoints, per-tenant test-caller endpoint, register→Dial→AudioSocket
  dialplan with h-extension reporting — validated against a real Asterisk 20
  container (modules, dialplan, endpoints all load)
- docker-compose 'voice' profile (voice server + Asterisk), Dockerfile.voice,
  docs/VOICE_TESTING.md softphone runbook
- 16 new tests incl. full fake-call e2e and a real-TCP AudioSocket wire test

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

alembic/versions/9dce40d5c9ce_call_registrations.py

@@ -0,0 +1,41 @@
+"""call registrations
+
+Revision ID: 9dce40d5c9ce
+Revises: 62fcb10345fa
+Create Date: 2026-07-11 10:58:21.464071
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+revision: str = '9dce40d5c9ce'
+down_revision: Union[str, None] = '62fcb10345fa'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_table('call_registrations',
+    sa.Column('id', sa.Uuid(), nullable=False),
+    sa.Column('tenant_id', sa.Uuid(), nullable=False),
+    sa.Column('caller_msisdn', sa.String(length=30), nullable=False),
+    sa.Column('created_at', sa.DateTime(timezone=True), nullable=False),
+    sa.Column('answered_by_human', sa.Boolean(), nullable=False),
+    sa.Column('handled_by_agent', sa.Boolean(), nullable=False),
+    sa.Column('finalized', sa.Boolean(), nullable=False),
+    sa.ForeignKeyConstraint(['tenant_id'], ['tenants.id'], ),
+    sa.PrimaryKeyConstraint('id')
+    )
+    op.create_index(op.f('ix_call_registrations_tenant_id'), 'call_registrations', ['tenant_id'], unique=False)
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_index(op.f('ix_call_registrations_tenant_id'), table_name='call_registrations')
+    op.drop_table('call_registrations')
+    # ### end Alembic commands ###