Add brain memory services and APIs

Introduce the backend pieces for brain memory ingestion, routing, and
system telemetry so the new knowledge workflows can project data into a
brain view. The supporting tests lock in the new behavior and keep the
expanded backend surface stable.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/models/__init__.py

@@ -7,6 +7,15 @@ from app.models.agent import Agent, AgentMessage
 from app.models.conversation import Conversation, Message
 from app.models.knowledge_graph import KGNode, KGEdge
 from app.models.memory import MemorySummary, UserMemory
+from app.models.brain import (
+    BrainEvent,
+    BrainCandidate,
+    BrainMemory,
+    BrainTag,
+    brain_event_tags,
+    brain_memory_tags,
+    brain_memory_sources,
+)
 from app.models.todo import DailyTodo, TodoSource
 from app.models.log import Log, LogType, LogLevel
 
@@ -27,6 +36,13 @@ __all__ = [
     "KGEdge",
     "MemorySummary",
     "UserMemory",
+    "BrainEvent",
+    "BrainCandidate",
+    "BrainMemory",
+    "BrainTag",
+    "brain_event_tags",
+    "brain_memory_tags",
+    "brain_memory_sources",
     "DailyTodo",
     "TodoSource",
     "Log",