Spike 61: filesystem watcher and UI simplification

Add notify-based filesystem watcher for .story_kit/work/ that
auto-commits changes with deterministic messages and broadcasts
events over WebSocket. Push full pipeline state (Upcoming, Current,
QA, To Merge) to frontend on connect and after every watcher event.

Strip dead UI: remove ReviewPanel, GatePanel, TodoPanel,
UpcomingPanel and all associated REST polling. Replace with 4
generic StagePanel components driven by WebSocket. Simplify
AgentPanel to roster-only.

Delete all 11 workflow HTTP endpoints and 16 request/response types
from the server. Clean dead code from workflow module. MCP tools
call Rust functions directly and need none of the HTTP layer.

Net: ~4,100 lines deleted, ~400 added.

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

server/src/http/context.rs

@@ -1,9 +1,11 @@
 use crate::agents::AgentPool;
+use crate::io::watcher::WatcherEvent;
 use crate::state::SessionState;
 use crate::store::JsonFileStore;
 use crate::workflow::WorkflowState;
 use poem::http::StatusCode;
 use std::sync::Arc;
+use tokio::sync::broadcast;
 
 #[derive(Clone)]
 pub struct AppContext {
@@ -11,6 +13,9 @@ pub struct AppContext {
     pub store: Arc<JsonFileStore>,
     pub workflow: Arc<std::sync::Mutex<WorkflowState>>,
     pub agents: Arc<AgentPool>,
+    /// Broadcast channel for filesystem watcher events. WebSocket handlers
+    /// subscribe to this to push lifecycle notifications to connected clients.
+    pub watcher_tx: broadcast::Sender<WatcherEvent>,
 }
 
 #[cfg(test)]
@@ -19,11 +24,13 @@ impl AppContext {
         let state = SessionState::default();
         *state.project_root.lock().unwrap() = Some(project_root.clone());
         let store_path = project_root.join(".story_kit_store.json");
+        let (watcher_tx, _) = broadcast::channel(64);
         Self {
             state: Arc::new(state),
             store: Arc::new(JsonFileStore::new(store_path).unwrap()),
             workflow: Arc::new(std::sync::Mutex::new(WorkflowState::default())),
             agents: Arc::new(AgentPool::new(3001)),
+            watcher_tx,
         }
     }
 }