llm: switch Skald to agent-loop Model clients; drop llm-client (phase 1, D13)

The LLM call path now runs on the agent-loop crate's clients and trait:

- core-api: BuiltLlmClient.client is Arc<dyn agent_loop::model::Model>;
  chatbot.rs (ChatbotClient + wire types) deleted; APP_NAME re-exported
  from agent-loop
- providers (openai/anthropic/ollama/openrouter/requesty/declared) build
  OpenAiModel/AnthropicModel/OllamaModel with the model's wire id
- LoggingModel decorator (llm/logging.rs) replaces LoggingChatbotClient;
  per-request correlation (session/stack/user) travels in the new
  ModelRequest.log field, never sent to providers
- llm_call/llm_loop/compactor speak Model::complete + ModelResponse;
  retriability via Model::is_retriable (structured status, B6 rule now
  the crate's default); payload persistence reads RawMeta off
  ModelResponse/ModelError
- crates/llm-client and skald-core/src/chatbot deleted

Full workspace test suite green (incl. 162 skald-core + 32 agent-loop).

crates/skald-core/src/llm/mod.rs

@@ -1,10 +1,12 @@
 pub(crate) mod db;
+pub mod logging;
 pub mod manager;
 pub mod providers;
 
 use std::sync::Arc;
 
-use crate::chatbot::ChatbotClient;
+use agent_loop::model::Model;
+
 use crate::provider::ServiceType;
 
 pub use core_api::provider::{LlmProviderRecord, LlmModelRecord, LlmStrength, ReasoningMode};
@@ -13,7 +15,7 @@ pub use manager::{LlmManager, sort_models_for_agent};
 /// A resolved, ready-to-use LLM client with its associated metadata.
 #[derive(Clone)]
 pub struct LlmEntry {
-    pub client:          Arc<dyn ChatbotClient>,
+    pub client:          Arc<dyn Model>,
     pub model:           String,
     pub model_db_id:     i64,
     pub strength:        Option<LlmStrength>,