chore(automation): trim docstrings to intent only

Cut the docstrings and Field(description=...) text across the entire
automations/ tree down to single-line intent statements, matching the
multi_agent_chat conciseness style:

- Module docstrings: one line stating what the file is.
- Class docstrings: deleted when the class name + module docstring
  already cover intent; kept only where they add a constraint or
  rationale not visible in the signature.
- Pydantic Field descriptions: short noun phrases / clauses, not
  full sentences. Reasoning that belonged in the design plan moved
  out of the code.
- Enum values: per-value docstrings replaced with terse inline
  comments where the meaning isn't obvious from the name.

Behaviour is unchanged. The same 33 files, same public surface, same
imports — verified by re-running the 10-point registry smoke test and
the 8-point schema round-trip / constraint suite from commits 9 and
10.

LOC: 1180 → 691 (-42%).

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

@@ -1,4 +1,4 @@
-"""``AutomationTrigger`` table — one row per (automation, trigger-instance) pair."""
+"""``automation_triggers`` table — one row per (automation, trigger-instance) pair."""
 
 from __future__ import annotations
 
@@ -18,14 +18,6 @@ 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(
@@ -51,7 +43,4 @@ class AutomationTrigger(BaseModel, TimestampMixin):
         index=True,
     )
 
-    last_fired_at = Column(
-        TIMESTAMP(timezone=True),
-        nullable=True,
-    )
+    last_fired_at = Column(TIMESTAMP(timezone=True), nullable=True)