refactor(agents): introduce chat/ category; dissolve top-level agents/shared

Recursive shared-folder rule: a shared/ must be shared by ALL siblings at its
level. The kernel (context, compaction, retry_after, web_search) was shared by
only 2 of the agents -- anonymous_chat + multi_agent_chat -- never by podcaster
or video_presentation. Those 2 are the "chat" category, so their shared code
belongs in that category's shared/, not the top-level one.

  app/agents/anonymous_chat/   -> app/agents/chat/anonymous_chat/
  app/agents/multi_agent_chat/ -> app/agents/chat/multi_agent_chat/
  app/agents/shared/           -> app/agents/chat/shared/   (anon<->mac kernel)

Top-level app/agents/shared/ is gone: nothing was shared across all three
categories (chat / podcaster / video_presentation).

~289 import sites rewritten (app.agents.{anonymous_chat,multi_agent_chat,shared}
-> app.agents.chat.*); all moves are git renames (history preserved).
app/agents/ now: chat/, podcaster/, video_presentation/, runtime/.

surfsense_backend/tests/integration/agents/multi_agent_chat/test_agent_turn.py

@@ -16,7 +16,7 @@ import pytest
 from langchain_core.messages import AIMessage, HumanMessage, ToolMessage
 from langgraph.checkpoint.memory import InMemorySaver
 
-from app.agents.multi_agent_chat import create_multi_agent_chat_deep_agent
+from app.agents.chat.multi_agent_chat import create_multi_agent_chat_deep_agent
 from app.services.connector_service import ConnectorService
 from tests.integration.harness import (
     ScriptedTurn,

surfsense_backend/tests/integration/agents/multi_agent_chat/test_kb_filesystem_cloud.py

@@ -20,14 +20,14 @@ from langchain.agents import create_agent
 from langchain_core.messages import HumanMessage, ToolMessage
 from langgraph.checkpoint.memory import InMemorySaver
 
-from app.agents.multi_agent_chat.shared.filesystem_selection import (
+from app.agents.chat.multi_agent_chat.shared.filesystem_selection import (
     FilesystemMode,
     FilesystemSelection,
 )
-from app.agents.multi_agent_chat.shared.middleware.filesystem import (
+from app.agents.chat.multi_agent_chat.shared.middleware.filesystem import (
     build_filesystem_mw,
 )
-from app.agents.multi_agent_chat.shared.middleware.filesystem.backends.resolver import (
+from app.agents.chat.multi_agent_chat.shared.middleware.filesystem.backends.resolver import (
     build_backend_resolver,
 )
 from tests.integration.harness import ScriptedTurn, build_scripted_harness

surfsense_backend/tests/integration/agents/multi_agent_chat/test_kb_filesystem_desktop.py

@@ -1,10 +1,10 @@
 """Real-behavior tests for the LIVE knowledge-base filesystem middleware (B).
 
-These exercise ``app.agents.multi_agent_chat.shared.middleware.filesystem`` —
+These exercise ``app.agents.chat.multi_agent_chat.shared.middleware.filesystem`` —
 the decomposed middleware + tools that production actually mounts on the
 knowledge_base subagent (via ``build_filesystem_mw``). The previous
 ``tests/unit/middleware/test_filesystem_*.py`` suite asserts a *dead twin*
-(``app.agents.shared.middleware.filesystem``) that is never instantiated, so the
+(``app.agents.chat.shared.middleware.filesystem``) that is never instantiated, so the
 live tool path had no real coverage.
 
 Strategy: mount the production ``build_filesystem_mw`` on a minimal
@@ -23,15 +23,15 @@ from langchain.agents import create_agent
 from langchain_core.messages import HumanMessage, ToolMessage
 from langgraph.checkpoint.memory import InMemorySaver
 
-from app.agents.multi_agent_chat.shared.filesystem_selection import (
+from app.agents.chat.multi_agent_chat.shared.filesystem_selection import (
     FilesystemMode,
     FilesystemSelection,
     LocalFilesystemMount,
 )
-from app.agents.multi_agent_chat.shared.middleware.filesystem import (
+from app.agents.chat.multi_agent_chat.shared.middleware.filesystem import (
     build_filesystem_mw,
 )
-from app.agents.multi_agent_chat.shared.middleware.filesystem.backends.resolver import (
+from app.agents.chat.multi_agent_chat.shared.middleware.filesystem.backends.resolver import (
     build_backend_resolver,
 )
 from tests.integration.harness import ScriptedTurn, build_scripted_harness