Stage 5: Alembic migrations, durable call rows, one transcript truth

Alembic replaces create_all as the schema authority: async env.py
against Base.metadata (CLI and in-app entry paths share it via
config.attributes["connection"]), an autogenerated baseline of the
create_all-era schema, and init_db now runs upgrade head — stamping
the baseline first on a pre-Alembic database so existing deployments
adopt cleanly. create_all remains for tests only.

Calls are durable from the start: CallManager gains an
on_call_created hook (wired to persist_call_on_create) that inserts
an in_progress CallRecord the moment a call is created;
persist_call_on_end finalizes that same row. A SIGKILL mid-call now
leaves an in_progress row instead of erasing the call from history
(verified live against the dev database).

One transcript representation: ActiveCall.transcript_chunks holds
TranscriptEntry (t_offset_ms, speaker, text) — add_transcript stamps
real offsets from connect time, receptionist passes speaker instead
of encoding it into "caller: ..." strings, persisted chunks carry
real seek offsets, and the dead CallRecord.transcript Text column is
dropped by migration. Device.is_online migrates String → Boolean
(with a USING cast for existing rows).

Model de-triplication: CallResponse/CallStatusResponse build via
from_call classmethods (one ActiveCall→response mapping);
DeviceStatus deleted — can_receive_call is a computed field on
Device and the list endpoint returns the domain model; all row↔dict
and row↔domain mapping now lives in call_persistence.py
(record_summary/record_detail/chunk_to_dict + device row functions).

New tests/test_data_layer.py: upgrade-head-matches-models,
pre-Alembic adoption, durable in_progress rows, end-without-create
fallback, transcript offsets, consolidated response models.

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

models/device.py

@@ -8,7 +8,7 @@ from datetime import datetime
 from enum import Enum
 from typing import Optional
 
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Field, computed_field
 
 
 class DeviceType(str, Enum):
@@ -43,6 +43,7 @@ class Device(DeviceBase):
     created_at: Optional[datetime] = None
     updated_at: Optional[datetime] = None
 
+    @computed_field  # serialized so API consumers see routability directly
     @property
     def can_receive_call(self) -> bool:
         """Can this device receive a call right now?"""
@@ -71,14 +72,3 @@ class DeviceUpdate(BaseModel):
     phone_number: Optional[str] = None
     priority: Optional[int] = None
     capabilities: Optional[list[str]] = None
-
-
-class DeviceStatus(BaseModel):
-    """Lightweight device status for list views."""
-
-    id: str
-    name: str
-    type: DeviceType
-    is_online: bool
-    last_seen: Optional[datetime] = None
-    can_receive_call: bool