Add db/ source files that were blocked by overly broad gitignore

The old `db/` pattern in .gitignore matched src/yc_bench/db/ too,
preventing all ORM models and session.py from being committed.
Previous commit fixed .gitignore to `/db/`; this adds the 10 missing files.

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

src/yc_bench/db/models/task.py

@@ -0,0 +1,140 @@
+from __future__ import annotations
+
+from enum import Enum
+from uuid import uuid4
+
+from sqlalchemy import BigInteger, Boolean, CheckConstraint, DateTime, Enum as SAEnum, ForeignKey, Integer, Numeric, String, Uuid, text
+from sqlalchemy.orm import mapped_column
+
+from ..base import Base
+from .company import Domain
+
+class TaskStatus(str, Enum):
+    MARKET = "market"
+    PLANNED = "planned"
+    ACTIVE = "active"
+    COMPLETED_SUCCESS = "completed_success"
+    COMPLETED_FAIL = "completed_fail"
+    CANCELLED = "cancelled"
+
+class Task(Base):
+    __tablename__ = "tasks"
+    __table_args__ = (
+        CheckConstraint("required_prestige >= 1 AND required_prestige <= 10", name="ck_tasks_required_prestige_range"),
+        CheckConstraint("skill_boost_pct >= 0", name="ck_tasks_skill_boost_pct_range"),
+        CheckConstraint("reward_funds_cents >= 0", name="ck_tasks_reward_funds_cents_gte_0"),
+        CheckConstraint("reward_prestige_delta >= 0 AND reward_prestige_delta <= 5", name="ck_tasks_reward_prestige_delta_range"),
+    )
+
+    id = mapped_column(
+        Uuid(as_uuid=True),
+        primary_key=True,
+        default=uuid4,
+    )
+    company_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("companies.id", ondelete="CASCADE"),
+        nullable=True,
+    )
+    status = mapped_column(
+        SAEnum(TaskStatus, name="task_status", values_callable=lambda e: [x.value for x in e]),
+        nullable=False,
+        default=TaskStatus.MARKET,
+    )
+    title = mapped_column(
+        String(255),
+        nullable=False,
+    )
+    description = mapped_column(
+        String,
+        nullable=False,
+    )
+    required_prestige = mapped_column(
+        Integer,
+        nullable=False,
+    )
+    reward_funds_cents = mapped_column(
+        BigInteger,
+        nullable=False,
+    )
+    reward_prestige_delta = mapped_column(
+        Numeric(6, 3),
+        nullable=False,
+    )
+    skill_boost_pct = mapped_column(
+        Numeric(6, 4),
+        nullable=False,
+    )
+    accepted_at = mapped_column(
+        DateTime(timezone=True),
+        nullable=True,
+    )
+    deadline = mapped_column(
+        DateTime(timezone=True),
+        nullable=True,
+    )
+    completed_at = mapped_column(
+        DateTime(timezone=True),
+        nullable=True,
+    )
+    success = mapped_column(
+        Boolean,
+        nullable=True,
+    )
+    halfway_event_emitted = mapped_column(
+        Boolean,
+        nullable=False,
+        default=False,
+        server_default=text("false"),
+    )
+
+class TaskRequirement(Base):
+    __tablename__ = "task_requirements"
+    __table_args__ = (
+        CheckConstraint("required_qty >= 200 AND required_qty <= 3000", name="ck_task_requirements_required_qty_range"),
+        CheckConstraint("completed_qty >= 0", name="ck_task_requirements_completed_qty_gte_0"),
+        CheckConstraint("completed_qty <= required_qty", name="ck_task_requirements_completed_qty_lte_required_qty"),
+    )
+
+    task_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("tasks.id", ondelete="CASCADE"),
+        primary_key=True,
+        nullable=False,
+    )
+    domain = mapped_column(
+        SAEnum(Domain, name="domain", values_callable=lambda e: [x.value for x in e]),
+        primary_key=True,
+        nullable=False,
+    )
+    required_qty = mapped_column(
+        Numeric(14, 4),
+        nullable=False,
+    )
+    completed_qty = mapped_column(
+        Numeric(14, 4),
+        nullable=False,
+        default=0,
+    )
+
+class TaskAssignment(Base):
+    __tablename__ = "task_assignments"
+
+    task_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("tasks.id", ondelete="CASCADE"),
+        primary_key=True,
+        nullable=False,
+    )
+    employee_id = mapped_column(
+        Uuid(as_uuid=True),
+        ForeignKey("employees.id", ondelete="CASCADE"),
+        primary_key=True,
+        nullable=False,
+    )
+    assigned_at = mapped_column(
+        DateTime(timezone=True),
+        nullable=False,
+    )
+
+__all__ = ["TaskStatus", "Task", "TaskRequirement", "TaskAssignment"]