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/unit/services/test_image_gen_api_base_defense.py

@@ -91,7 +91,7 @@ async def test_global_openrouter_image_gen_sets_api_base_when_config_empty():
 async def test_generate_image_tool_global_sets_api_base_when_config_empty():
     """Same defense at the agent tool entry point — both surfaces share
     the same OpenRouter config payloads."""
-    from app.agents.multi_agent_chat.subagents.builtins.deliverables.tools import (
+    from app.agents.chat.multi_agent_chat.subagents.builtins.deliverables.tools import (
         generate_image as gi_module,
     )
 

surfsense_backend/tests/unit/services/test_supports_image_input.py

@@ -227,7 +227,7 @@ global_llm_configs:
 
 
 def test_agent_config_from_yaml_explicit_overrides_resolver():
-    from app.agents.multi_agent_chat.shared.llm_config import AgentConfig
+    from app.agents.chat.multi_agent_chat.shared.llm_config import AgentConfig
 
     cfg_text_only = AgentConfig.from_yaml_config(
         {
@@ -256,7 +256,7 @@ def test_agent_config_from_yaml_explicit_overrides_resolver():
 def test_agent_config_from_yaml_unannotated_uses_resolver():
     """Without an explicit YAML key, AgentConfig defers to the catalog
     resolver — for ``gpt-4o`` LiteLLM's map says supports_vision=True."""
-    from app.agents.multi_agent_chat.shared.llm_config import AgentConfig
+    from app.agents.chat.multi_agent_chat.shared.llm_config import AgentConfig
 
     cfg = AgentConfig.from_yaml_config(
         {
@@ -275,7 +275,7 @@ def test_agent_config_auto_mode_supports_image_input():
     so users can keep their selection on Auto with a vision-capable
     deployment somewhere in the pool. The router's own `allowed_fails`
     handles non-vision deployments via fallback."""
-    from app.agents.multi_agent_chat.shared.llm_config import AgentConfig
+    from app.agents.chat.multi_agent_chat.shared.llm_config import AgentConfig
 
     auto = AgentConfig.from_auto_mode()
     assert auto.supports_image_input is True

surfsense_backend/tests/unit/services/test_vision_llm_api_base_defense.py

@@ -61,7 +61,7 @@ async def test_get_vision_llm_global_openrouter_sets_api_base():
             return_value=cfg,
         ),
         patch(
-            "app.agents.multi_agent_chat.shared.llm_config.SanitizedChatLiteLLM",
+            "app.agents.chat.multi_agent_chat.shared.llm_config.SanitizedChatLiteLLM",
             new=FakeSanitized,
         ),
     ):