feat(automation): add empty Capability / Action / Trigger registries

Three registries under app/automations/registries/, each as its own
folder with the same SRP-per-file split (types.py for the dataclass,
store.py for the in-memory dict + register/get/all functions). All
three start empty; concrete entries land when the user signs off on
which capabilities / actions / triggers to include (step 2).

Capability (locked at v1-minimum five fields — see commit 2):
  - id, description, input_schema, output_schema, handler
  - CapabilityHandler = Callable[[dict[str, Any]], Awaitable[Any]]
  - Frozen, slotted dataclass (immutable post-registration).

ActionDefinition (v1-trim of design plan §4):
  - type, name, description, config_schema, handler
  - Defers output_contract (handled per-step by agent_task's
    config.output_schema), uses_capabilities (no static analysis
    needed until >1 action ships), and produces_artifacts (deferred
    alongside the artifact pipeline).

TriggerDefinition (declarative, no handler):
  - type, description, config_schema, payload_schema
  - No handler field — firing is a single dispatcher's
    responsibility, not a per-trigger one.

store.py contract for all three:
  - register_*: idempotent at process startup, raises on duplicate
  - get_*: returns None on miss
  - all_*: returns a defensive copy of the registry dict

Verified by an inline smoke test (10 checks): empty initial state,
registration and lookup work, duplicates raise, frozen dataclasses
reject mutation, snapshots are copies, handlers are awaitable.

Isolation invariant audit: grep across the full app/automations/
tree shows only three app.* imports, all of them
``from app.db import BaseModel, TimestampMixin`` in the model files.
No imports from app.agents.*, app.services.*, app.tasks.*,
app.routes.*, or any other business-logic module.

surfsense_backend/app/automations/registries/triggers/__init__.py

@@ -2,4 +2,12 @@
 
 from __future__ import annotations
 
-__all__: list[str] = []
+from .store import all_triggers, get_trigger, register_trigger
+from .types import TriggerDefinition
+
+__all__ = [
+    "TriggerDefinition",
+    "all_triggers",
+    "get_trigger",
+    "register_trigger",
+]

surfsense_backend/app/automations/registries/triggers/store.py

@@ -0,0 +1,33 @@
+"""Trigger registry: in-memory dict + ``register_trigger`` API."""
+
+from __future__ import annotations
+
+from .types import TriggerDefinition
+
+_REGISTRY: dict[str, TriggerDefinition] = {}
+
+
+def register_trigger(trigger: TriggerDefinition) -> None:
+    """Add a trigger to the in-memory registry.
+
+    Raises ``ValueError`` on duplicate ``type`` — registration runs
+    once per process, so a duplicate is always a bug.
+    """
+
+    if trigger.type in _REGISTRY:
+        raise ValueError(
+            f"Trigger already registered: {trigger.type!r}"
+        )
+    _REGISTRY[trigger.type] = trigger
+
+
+def get_trigger(trigger_type: str) -> TriggerDefinition | None:
+    """Look up one trigger by type. Returns ``None`` on miss."""
+
+    return _REGISTRY.get(trigger_type)
+
+
+def all_triggers() -> dict[str, TriggerDefinition]:
+    """Snapshot of the registry as a defensive copy."""
+
+    return dict(_REGISTRY)

surfsense_backend/app/automations/registries/triggers/types.py

@@ -0,0 +1,35 @@
+"""``TriggerDefinition`` dataclass — declarative trigger metadata, no handler."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Any
+
+
+@dataclass(frozen=True, slots=True)
+class TriggerDefinition:
+    """A trigger type the dispatcher knows how to fire.
+
+    Triggers are purely declarative: the dispatcher (a single
+    process-wide component, not a per-type handler) reads the
+    ``automation_triggers`` table and decides when each row should
+    fire. The trigger's job here is to declare its input/output
+    contract:
+
+    - ``config_schema``: JSON Schema for the persisted
+      ``AutomationTrigger.config`` — used by the form editor and
+      validated on save.
+    - ``payload_schema``: JSON Schema for the payload the dispatcher
+      will deliver to the executor at fire time (e.g., a schedule
+      trigger emits ``fired_at`` / ``scheduled_for`` /
+      ``last_fired_at``).
+
+    No ``handler`` field — firing is a dispatcher responsibility,
+    not a per-trigger one. This keeps the dispatcher single and
+    leaves trigger types as pure metadata.
+    """
+
+    type: str
+    description: str
+    config_schema: dict[str, Any]
+    payload_schema: dict[str, Any]