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).

Cargo.toml

@@ -5,7 +5,6 @@ members = [
     "crates/skald-core",
     "crates/skald-setup",
     "crates/honcho-client",
-    "crates/llm-client",
     "crates/core-api",
     "crates/mcp-client",
     "crates/plugin-tailscale-remote",
@@ -74,7 +73,6 @@ tracing-appender   = "0.2"
 chrono             = { version = "0.4", default-features = false, features = ["clock", "std"] }
 notify             = "8"
 honcho-client            = { path = "crates/honcho-client" }
-llm-client               = { path = "crates/llm-client" }
 core-api                 = { path = "crates/core-api" }
 mcp-client               = { path = "crates/mcp-client" }
 plugin-tailscale-remote          = { path = "crates/plugin-tailscale-remote" }