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/enums/automation_status.py

@@ -0,0 +1,18 @@
+"""``AutomationStatus`` — lifecycle of a stored automation definition."""
+
+from __future__ import annotations
+
+from enum import StrEnum
+
+
+class AutomationStatus(StrEnum):
+    """Status of an automation in the registry.
+
+    ``active``   — eligible to fire from its triggers.
+    ``paused``   — definition retained, triggers do not fire.
+    ``archived`` — kept for run history only; no edits, no fires.
+    """
+
+    ACTIVE = "active"
+    PAUSED = "paused"
+    ARCHIVED = "archived"