feat(shared): cross-cutting plumbing and pure domain layer

Typed pydantic-settings config, structlog JSON logging with request/trace id
propagation and redaction of phone numbers, tokens and face keys, the unified
response envelope and error-code table from 架构文档 §9.2, async SQLAlchemy
session management, ORM models for the eight foundation tables, and the
OpenTelemetry/Prometheus wiring.

packages/domain stays pure logic -- snowflake ids, the quota three-phase
protocol and the tk_task state machine -- so it can be tested without a
database and is held to mypy strict.

packages/domain/task/state.py

@@ -0,0 +1,76 @@
+"""tk_task state machine — pure logic (架构文档 §6.2 task 域, FR-TASK-01).
+
+统一任务中心 is the only long-running-task view in the system; every long task
+(report / tryon / hairstyle / matting / render) moves through these states.
+"""
+
+from __future__ import annotations
+
+from enum import StrEnum
+
+from packages.domain.errors import InvalidTaskTransitionError
+
+
+class TaskStatus(StrEnum):
+    PENDING = "pending"  # created, quota reserved, not yet queued
+    QUEUED = "queued"  # handed to Celery
+    RUNNING = "running"
+    SUCCEEDED = "succeeded"
+    FAILED = "failed"
+    CANCELED = "canceled"
+
+
+class TaskType(StrEnum):
+    REPORT = "report"
+    TRYON = "tryon"
+    HAIRSTYLE = "hairstyle"
+    MATTING = "matting"
+    RENDER = "render"
+    PING = "ping"  # scaffold-only: proves the async path end to end
+
+
+TERMINAL_STATUSES: frozenset[TaskStatus] = frozenset(
+    {TaskStatus.SUCCEEDED, TaskStatus.FAILED, TaskStatus.CANCELED}
+)
+
+#: Refunds are owed for every terminal state other than success (FR-TRY-05).
+REFUNDABLE_STATUSES: frozenset[TaskStatus] = frozenset({TaskStatus.FAILED, TaskStatus.CANCELED})
+
+ALLOWED_TRANSITIONS: dict[TaskStatus, frozenset[TaskStatus]] = {
+    TaskStatus.PENDING: frozenset({TaskStatus.QUEUED, TaskStatus.FAILED, TaskStatus.CANCELED}),
+    TaskStatus.QUEUED: frozenset({TaskStatus.RUNNING, TaskStatus.FAILED, TaskStatus.CANCELED}),
+    TaskStatus.RUNNING: frozenset(
+        {TaskStatus.SUCCEEDED, TaskStatus.FAILED, TaskStatus.CANCELED, TaskStatus.QUEUED}
+    ),
+    TaskStatus.SUCCEEDED: frozenset(),
+    TaskStatus.FAILED: frozenset({TaskStatus.QUEUED}),  # retry re-queues
+    TaskStatus.CANCELED: frozenset(),
+}
+
+
+def can_transition(current: TaskStatus, target: TaskStatus) -> bool:
+    return target in ALLOWED_TRANSITIONS[current]
+
+
+def assert_transition(current: TaskStatus, target: TaskStatus) -> None:
+    if not can_transition(current, target):
+        raise InvalidTaskTransitionError(current=current.value, target=target.value)
+
+
+def is_terminal(status: TaskStatus) -> bool:
+    return status in TERMINAL_STATUSES
+
+
+def needs_refund(status: TaskStatus) -> bool:
+    return status in REFUNDABLE_STATUSES
+
+
+def progress_for(status: TaskStatus) -> int:
+    return {
+        TaskStatus.PENDING: 0,
+        TaskStatus.QUEUED: 5,
+        TaskStatus.RUNNING: 50,
+        TaskStatus.SUCCEEDED: 100,
+        TaskStatus.FAILED: 100,
+        TaskStatus.CANCELED: 100,
+    }[status]