Add GET /api/v1/auth/count endpoint and first-run routing in Android app

Server: expose a public countUsers endpoint (GET /api/v1/auth/count)
so mobile clients can detect first-run (count=0) without a session.
Android: wire countUsers via DioPlayerApiClient, add firstRunProvider
(FutureProvider), update go_router redirect to drive /bootstrap vs /login
based on the count, rework LoginScreen to handle loading/error states, and
add widget tests for the new login screen and smoke-test updates.

Fix review issues: correct FutureProvider cache-lifetime comment in
first_run_provider.dart; add TestServer_CountUsers covering zero-users
and users-exist cases to handlers_test.go.

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

1 files changed, 3 insertions, 0 deletions

diff --git a/player-server/internal/api/server.go b/player-server/internal/api/server.go
index fa2ca74..e87c532 100644
--- a/player-server/internal/api/server.go
+++ b/player-server/internal/api/server.go
@@ -225,6 +225,9 @@ func (s *Server) routesPublic() {
 	s.handlePublicFunc("/api/v1/auth/bootstrap", publicMethod(http.MethodPost, s.handleBootstrap))
 	s.handlePublicFunc("/api/login", publicMethod(http.MethodPost, s.handleLogin))
 	s.handlePublicFunc("/api/v1/auth/login", publicMethod(http.MethodPost, s.handleLogin))
+	// Public user-count endpoint: mobile clients query this on first launch to
+	// decide whether to show the bootstrap screen (count=0) or the login screen.
+	s.handlePublicFunc("/api/v1/auth/count", publicMethod(http.MethodGet, s.handleCountUsers))
 	s.handlePublicFunc("/healthz", publicMethod(http.MethodGet, s.handleHealthz))
 	s.handlePublicFunc("/readyz", publicMethod(http.MethodGet, s.handleReadyz))
 }