feat(web): service page, manual update, jobs list and live job log (#7)

Also publishes the jobs topic on agent revoke and updates the agent
snippet to mount stacks read-write at the same path.

internal/master/webauth/auth.go

@@ -157,7 +157,7 @@ func (a *Auth) Require(next http.Handler) http.Handler {
 				return
 			}
 		}
-		next.ServeHTTP(w, r.WithContext(context.WithValue(r.Context(), sessionKey{}, sess)))
+		next.ServeHTTP(w, r.WithContext(WithSession(r.Context(), sess)))
 	})
 }
 
@@ -171,6 +171,11 @@ func (a *Auth) session(r *http.Request) (model.Session, error) {
 
 type sessionKey struct{}
 
+// WithSession returns ctx carrying sess, as Require does.
+func WithSession(ctx context.Context, sess model.Session) context.Context {
+	return context.WithValue(ctx, sessionKey{}, sess)
+}
+
 // SessionFrom returns the session Require stored in ctx.
 func SessionFrom(ctx context.Context) (model.Session, bool) {
 	s, ok := ctx.Value(sessionKey{}).(model.Session)