feat: wire fps diagnostics into video present/init

Also fixes frame_budget_ns being left unset when vsync paces
presentation without an explicit sleep (present_fn == present), and
exposes it as skele_frame_budget_ms for reporting alongside the
sleep-based capped path.

src/platform/client/video/gl.c

@@ -1,5 +1,6 @@
 #include "client/video.h"
 #include "clock.h"
+#include "fps.h"
 #include "skele.h"
 #include <SDL3/SDL.h>
 #include <stk/stk_log.h>
@@ -49,7 +50,9 @@ static void apply_present_mode(void)
 
 	cap = configured_max_fps;
 
-	if (cap == SKELE_VIDEO_FPS_UNCAPPED || (vsync_active && !cap)) {
+	if (cap == SKELE_VIDEO_FPS_UNCAPPED) {
+		frame_budget_ns = 0;
+		skele_frame_budget_ms = 0.0f;
 		present_fn = present;
 		return;
 	}
@@ -63,8 +66,9 @@ static void apply_present_mode(void)
 	}
 
 	frame_budget_ns = 1000000000ULL / cap;
+	skele_frame_budget_ms = frame_budget_ns / 1e6f;
 	last_present_ns = skele_time_ns();
-	present_fn = present_capped;
+	present_fn = vsync_active ? present : present_capped;
 }
 
 static uint8_t max_scale(uint16_t rw, uint16_t rh)
@@ -219,6 +223,7 @@ uint8_t skele_video_init(skele_video_config_t cfg)
 	apply_present_mode();
 
 	SDL_ShowWindow(window);
+	skele_fps_init();
 	return SKELE_INIT_SUCCESS;
 }
 
@@ -237,7 +242,11 @@ void skele_video_shutdown(void)
 	is_fullscreen = 0;
 }
 
-void skele_video_present(void) { present_fn(); }
+void skele_video_present(void)
+{
+	present_fn();
+	skele_fps_frame_mark();
+}
 uint8_t skele_video_using_vsync(void) { return vsync_active; }
 
 void skele_video_set_vsync(uint8_t enabled)