refactor(agents): promote anonymous_agent to its own anonymous_chat/ package (slice 8)

The anonymous / free-chat agent is a distinct live agent (not part of the
single-agent stack and not shared infrastructure), so it gets its own top-level
package app/agents/anonymous_chat/ (sibling to multi_agent_chat). Moved
new_chat/anonymous_agent.py -> anonymous_chat/agent.py with a package __init__
re-exporting create_anonymous_chat_agent + build_anonymous_system_prompt.

Repointed its only new_chat import (the context shim) to app.agents.shared.context
and updated the single importer (anonymous_chat_routes). The test_import_all
guard auto-discovers the new package via pkgutil.walk_packages, so it is covered.

surfsense_backend/app/agents/anonymous_chat/__init__.py

@@ -0,0 +1,14 @@
+"""Anonymous / free-chat agent.
+
+The no-login chat experience: a deliberately minimal agent that bypasses the
+full SurfSense deep-agent stack (filesystem, knowledge-base persistence,
+subagents, skills, memory) and answers with an optional ``web_search`` tool and
+an optional read-only uploaded document. See :mod:`.agent` for details.
+"""
+
+from app.agents.anonymous_chat.agent import (
+    build_anonymous_system_prompt,
+    create_anonymous_chat_agent,
+)
+
+__all__ = ["build_anonymous_system_prompt", "create_anonymous_chat_agent"]

surfsense_backend/app/agents/anonymous_chat/agent.py

@@ -27,7 +27,7 @@ from langchain.agents.middleware import (
 from langchain_core.language_models import BaseChatModel
 from langgraph.types import Checkpointer
 
-from app.agents.new_chat.context import SurfSenseContextSchema
+from app.agents.shared.context import SurfSenseContextSchema
 from app.agents.shared.middleware import (
     RetryAfterMiddleware,
     create_surfsense_compaction_middleware,

surfsense_backend/app/routes/anonymous_chat_routes.py

@@ -351,7 +351,7 @@ async def stream_anonymous_chat(
     async def _generate():
         from langchain_core.messages import AIMessage, HumanMessage
 
-        from app.agents.new_chat.anonymous_agent import create_anonymous_chat_agent
+        from app.agents.anonymous_chat import create_anonymous_chat_agent
         from app.agents.shared.checkpointer import get_checkpointer
         from app.db import shielded_async_session
         from app.services.new_streaming_service import VercelStreamingService