feat(automation): add SQLAlchemy models for the three v1 tables

Three enums (one file each) plus three models (one file each), all
under app/automations/persistence/. The module imports from app.db
only (Base/BaseModel/TimestampMixin and FK targets searchspaces.id /
user.id); no business-logic imports.

Enums:
  - AutomationStatus: active | paused | archived
  - RunStatus: pending | running | succeeded | failed | cancelled
    | timed_out
  - TriggerType: schedule | manual (Phase-2/3 add webhook | event)

Models:
  - Automation: search_space-scoped, created_by_user_id (SET NULL),
    name + description, status enum, definition JSONB, version int,
    updated_at with onupdate.
  - AutomationTrigger: FK → automations (CASCADE), type enum, config
    JSONB, enabled bool, last_fired_at. Webhook secret_hash is omitted
    until Phase 2.
  - AutomationRun: FK → automations (CASCADE), nullable trigger_id
    (SET NULL — null = manual via UI), status enum,
    definition_snapshot for immutable history, trigger_payload /
    resolved_inputs / step_results / output / artifacts / error JSONB
    columns, started_at / finished_at timestamps, agent_session_id for
    linking to the LangGraph trace. cost_usd column omitted until at
    least one v1 capability records token-level cost.

Verified: Base.metadata exposes all three table names; columns and
enums introspect as documented; no linter errors.

surfsense_backend/app/automations/persistence/models/run.py

@@ -0,0 +1,72 @@
+"""``AutomationRun`` table — the immutable per-fire execution record."""
+
+from __future__ import annotations
+
+from sqlalchemy import (
+    TIMESTAMP,
+    Column,
+    Enum as SQLAlchemyEnum,
+    ForeignKey,
+    Integer,
+    String,
+)
+from sqlalchemy.dialects.postgresql import JSONB
+
+from app.db import BaseModel, TimestampMixin
+
+from ..enums.run_status import RunStatus
+
+
+class AutomationRun(BaseModel, TimestampMixin):
+    """One execution of an automation.
+
+    Every fire of any trigger inserts exactly one row here. The row is
+    immutable from the user's perspective — the executor only updates
+    ``status``, ``step_results``, ``output``, ``artifacts``, ``error``,
+    ``started_at``, ``finished_at`` as the run progresses; the
+    ``definition_snapshot`` is locked at fire time so the user can always
+    see exactly what code path executed for any historical run.
+    """
+
+    __tablename__ = "automation_runs"
+
+    automation_id = Column(
+        Integer,
+        ForeignKey("automations.id", ondelete="CASCADE"),
+        nullable=False,
+        index=True,
+    )
+
+    trigger_id = Column(
+        Integer,
+        ForeignKey("automation_triggers.id", ondelete="SET NULL"),
+        nullable=True,
+        index=True,
+    )
+
+    status = Column(
+        SQLAlchemyEnum(RunStatus, name="automation_run_status"),
+        nullable=False,
+        default=RunStatus.PENDING,
+        server_default=RunStatus.PENDING.value,
+        index=True,
+    )
+
+    definition_snapshot = Column(JSONB, nullable=False)
+
+    trigger_payload = Column(JSONB, nullable=True)
+
+    resolved_inputs = Column(JSONB, nullable=False, server_default="{}")
+
+    step_results = Column(JSONB, nullable=False, server_default="[]")
+
+    output = Column(JSONB, nullable=True)
+
+    artifacts = Column(JSONB, nullable=False, server_default="[]")
+
+    error = Column(JSONB, nullable=True)
+
+    started_at = Column(TIMESTAMP(timezone=True), nullable=True)
+    finished_at = Column(TIMESTAMP(timezone=True), nullable=True)
+
+    agent_session_id = Column(String(200), nullable=True)