feat(story-93): expose server logs to agents via get_server_logs MCP tool

- Add log_buffer module: bounded 1000-line ring buffer with push/get_recent API
- Add slog! macro: drop-in for eprintln! that also captures to ring buffer
- Replace all eprintln! calls across agents, watcher, search, chat, worktree, claude_code with slog!
- Add get_server_logs MCP tool: accepts count (1-500) and optional filter params
- 5 unit tests for log_buffer covering push/retrieve, eviction, filtering, count limits, empty buffer
- 262 tests passing, clippy clean

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

server/src/config.rs

@@ -1,3 +1,4 @@
+use crate::slog;
 use serde::Deserialize;
 use std::collections::HashSet;
 use std::path::Path;
@@ -123,7 +124,7 @@ impl ProjectConfig {
                 // Try legacy format.
                 if let Ok(legacy) = toml::from_str::<LegacyProjectConfig>(content)
                     && let Some(agent) = legacy.agent {
-                        eprintln!(
+                        slog!(
                             "[config] Warning: [agent] table is deprecated. \
                              Use [[agent]] array format instead."
                         );
@@ -142,7 +143,7 @@ impl ProjectConfig {
                 let legacy: LegacyProjectConfig =
                     toml::from_str(content).map_err(|e| format!("Parse config: {e}"))?;
                 if let Some(agent) = legacy.agent {
-                    eprintln!(
+                    slog!(
                         "[config] Warning: [agent] table is deprecated. \
                          Use [[agent]] array format instead."
                     );