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/trigger.py

@@ -0,0 +1,57 @@
+"""``AutomationTrigger`` table — one row per (automation, trigger-instance) pair."""
+
+from __future__ import annotations
+
+from sqlalchemy import (
+    TIMESTAMP,
+    Boolean,
+    Column,
+    Enum as SQLAlchemyEnum,
+    ForeignKey,
+    Integer,
+)
+from sqlalchemy.dialects.postgresql import JSONB
+
+from app.db import BaseModel, TimestampMixin
+
+from ..enums.trigger_type import TriggerType
+
+
+class AutomationTrigger(BaseModel, TimestampMixin):
+    """One trigger attached to an automation.
+
+    An automation may have multiple triggers — e.g. a ``schedule`` trigger
+    for the autonomous path and a ``manual`` trigger backing the UI's
+    "Run now" affordance. Each trigger's ``config`` is validated against
+    the registered ``TriggerDefinition.config_schema`` for its ``type``.
+    """
+
+    __tablename__ = "automation_triggers"
+
+    automation_id = Column(
+        Integer,
+        ForeignKey("automations.id", ondelete="CASCADE"),
+        nullable=False,
+        index=True,
+    )
+
+    type = Column(
+        SQLAlchemyEnum(TriggerType, name="automation_trigger_type"),
+        nullable=False,
+        index=True,
+    )
+
+    config = Column(JSONB, nullable=False)
+
+    enabled = Column(
+        Boolean,
+        nullable=False,
+        default=True,
+        server_default="true",
+        index=True,
+    )
+
+    last_fired_at = Column(
+        TIMESTAMP(timezone=True),
+        nullable=True,
+    )