agent: move oneshot execution from subconscious to agent module

Move agent execution machinery (run_one_agent, spawn_agent, PID
tracking) from subconscious/knowledge.rs to agent/oneshot.rs — the
agent module owns execution, subconscious owns scheduling and defs.

Delete subconscious/llm.rs — callers now use api::call_api_with_tools_sync
directly. Audit and compare inline the call; oneshot inlines tool
filtering.

Update all callers: consolidate, daemon, subconscious, cli/agent.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/agent/mod.rs

@@ -15,6 +15,7 @@
 
 pub mod api;
 pub mod context;
+pub mod oneshot;
 pub mod parsing;
 pub mod tools;
 pub mod training;