Story 26: Establish TDD workflow and quality gates

Add workflow engine with acceptance gates, test recording, and review
queue. Frontend displays gate status (blocked/ready), test summaries,
failing badges, and warnings. Proceed action is disabled when gates
are not met. Includes 13 unit tests (Vitest) and 9 E2E tests
(Playwright) covering all five acceptance criteria.

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

server/src/http/context.rs

@@ -1,5 +1,6 @@
 use crate::state::SessionState;
 use crate::store::JsonFileStore;
+use crate::workflow::WorkflowState;
 use poem::http::StatusCode;
 use std::sync::Arc;
 
@@ -7,6 +8,7 @@ use std::sync::Arc;
 pub struct AppContext {
     pub state: Arc<SessionState>,
     pub store: Arc<JsonFileStore>,
+    pub workflow: Arc<std::sync::Mutex<WorkflowState>>,
 }
 
 pub type OpenApiResult<T> = poem::Result<T>;