refactor(config): move embedder/l3 to top-level [embedder]/[l3] sections

They are shared infra (the orchestrator uses them for workflow repo-knowledge,
not just the router chat layer), so [router.embedder]/[router.l3] was misleading.
Loader/writer use the new names; legacy [router.*] still read as a fallback.
Also notes the STEERING LLM-reformulation cost as a ponytail follow-up.

docs/sample-config.toml

@@ -107,15 +107,18 @@ top_p = 0.9
 max_tokens = 1024
 max_per_run = 100
 
-[router.embedder]
+# Embedder + L3 vector memory. Shared infra: the orchestrator uses these for workflow
+# repo-knowledge retrieval, not just the router chat layer — hence top-level, not [router.*].
+# (Legacy [router.embedder] / [router.l3] are still read as a fallback.)
+[embedder]
 backend = "noop"               # or "llamacpp"
 dimension = 1536
 # url = "http://127.0.0.1:11000"
 # model_id = "nomic-embed-text"
 
-[router.l3]
+[l3]
 backend = "in_memory"          # or "turbovec"
-# persist_path = "~/.config/correx/router/l3/index.tq"
+# persist_path = "~/.config/correx/l3/index.tq"
 # python_executable = "python3"
 # script_path = "~/.config/correx/python/turbovec_sidecar.py"
 # dim = 1536