feat: add strategy market, login overlay, and registration limit page

- Add public strategy market API endpoint (/api/strategies/public)
- Add is_public and config_visible fields to Strategy model
- Add LoginRequiredOverlay component for unified auth prompts
- Add WhitelistFullPage for registration capacity limit
- Add StrategyMarketPage for browsing public strategies
- Unify navigation logic across HeaderBar, LandingPage, App
- Reduce klines API calls (fetch once on mount)
- Fix various page transition issues

api/server.go

@@ -127,6 +127,9 @@ func (s *Server) setupRoutes() {
 		api.GET("/klines", s.handleKlines)
 		api.GET("/symbols", s.handleSymbols)
 
+		// Public strategy market (no authentication required)
+		api.GET("/strategies/public", s.handlePublicStrategies)
+
 		// Authentication related routes (no authentication required)
 		api.POST("/register", s.handleRegister)
 		api.POST("/login", s.handleLogin)