feat(grpc): dev mode, agent prefix, system prompt, error UX

- gRPC dev_mode config: disables JWT auth, uses fixed dev identity
- Agent prefix (agents.agent_prefix): dev agents use "dev-sol-orchestrator"
  to avoid colliding with production on shared Mistral accounts
- Coding sessions use instructions (system prompt + coding addendum)
  with mistral-medium-latest for personality adherence
- Conversations API: don't send both model + agent_id (422 fix)
- GrpcState carries system_prompt + orchestrator_agent_id
- Session.end() keeps session active for reuse (not "ended")
- User messages posted as m.notice, assistant as m.text (role detection)
- History loaded from Matrix room on session resume
- Docker Compose local dev stack: OpenSearch 3 + Tuwunel + SearXNG
- Dev config: localhost URLs, dev_mode, opensearch-init.sh for ML setup

src/main.rs

@@ -256,6 +256,7 @@ async fn main() -> anyhow::Result<()> {
                 agent_tools,
                 &state.mistral,
                 &active_agents,
+                &config.agents.agent_prefix,
             )
             .await
         {
@@ -295,12 +296,16 @@ async fn main() -> anyhow::Result<()> {
 
     // Start gRPC server if configured
     if config.grpc.is_some() {
+        let orchestrator_id = state.conversation_registry.get_agent_id().await
+            .unwrap_or_default();
         let grpc_state = std::sync::Arc::new(grpc::GrpcState {
             config: config.clone(),
             tools: state.responder.tools(),
             store: store.clone(),
             mistral: state.mistral.clone(),
             matrix: matrix_client.clone(),
+            system_prompt: system_prompt_text.clone(),
+            orchestrator_agent_id: orchestrator_id,
         });
         tokio::spawn(async move {
             if let Err(e) = grpc::start_server(grpc_state).await {