story-kit: merge 93_story_expose_server_logs_to_agents_via_mcp

Adds log_buffer ring buffer and slog! macro for in-memory server log
capture, plus get_server_logs MCP tool for agents to read recent logs.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/main.rs

@@ -4,6 +4,7 @@ mod config;
 mod http;
 mod io;
 mod llm;
+pub mod log_buffer;
 mod state;
 mod store;
 mod workflow;
@@ -40,7 +41,7 @@ async fn main() -> Result<(), std::io::Error> {
         )
         .await
         .unwrap_or_else(|e| {
-            eprintln!("Warning: failed to auto-open project at {project_root:?}: {e}");
+            slog!("Warning: failed to auto-open project at {project_root:?}: {e}");
             project_root.to_string_lossy().to_string()
         });
 
@@ -85,11 +86,11 @@ async fn main() -> Result<(), std::io::Error> {
     // 2. Auto-assign free agents to remaining unassigned work in the pipeline.
     if let Some(root) = startup_root {
         tokio::spawn(async move {
-            eprintln!(
+            slog!(
                 "[startup] Reconciling completed worktrees from previous session."
             );
             startup_agents.reconcile_on_startup(&root).await;
-            eprintln!(
+            slog!(
                 "[auto-assign] Scanning pipeline stages for unassigned work."
             );
             startup_agents.auto_assign_available_work(&root).await;