fix(llm): send the provider model id on the wire, not the alias

LlmManager keys its model registry by llm_models.name (the user-facing
alias), and the kernel sent ModelHandle.id as the request's model field —
so the alias, not llm_models.model_id, went on the wire. A model worked
only while the alias was left equal to the model id; renaming it made
every provider reject the call (DeepInfra 404 model_not_found, DeepSeek
400 invalid_request_error).

ModelHandle gains an optional wire_id: the model identifier to put on the
wire when the selector's id is a bookkeeping key. The kernel and the
compaction summary call both send handle.wire_model(); SkaldSelector sets
wire_id from LlmEntry.model (llm_models.model_id). Everything else keeps
keying on the alias: the chat's model pin, health reporting, fallback
exclusion and request logging are untouched.

crates/agent-loop/src/testing.rs

@@ -118,9 +118,10 @@ impl Model for FakeModel {
 /// `requests()` afterwards).
 pub fn handle(fake: &std::sync::Arc<FakeModel>, id: &str) -> crate::model::ModelHandle {
     crate::model::ModelHandle {
-        id:    id.to_string(),
-        model: fake.clone(),
-        info:  crate::model::ModelInfo::default(),
+        id:      id.to_string(),
+        model:   fake.clone(),
+        info:    crate::model::ModelInfo::default(),
+        wire_id: None,
     }
 }