Fix NPC orientation (server yaw convention) and nameplate Y projection

coordinates.hpp: serverToCanonicalYaw now computes s - π/2 instead of π/2 - s.
The codebase uses atan2(-dy, dx) as its canonical yaw convention, where server
direction (cos s, sin s) in (server_X, server_Y) becomes (sin s, cos s) in
canonical after the X/Y swap, giving atan2(-cos s, sin s) = s - π/2.
canonicalToServerYaw is updated as its proper inverse: c + π/2.
The old formula (π/2 - s) was self-inverse and gave the wrong east/west facing
for any NPC not pointing north or south.

game_screen.cpp: Nameplate NDC→screen Y no longer double-inverts. The camera
bakes the Vulkan Y-flip into the projection matrix (NDC y=-1 = screen top,
y=+1 = screen bottom), so sy = (ndc.y*0.5 + 0.5) * screenH is correct.
The previous formula subtracted from 1.0 which reflected nameplates vertically.

src/ui/game_screen.cpp

@@ -4684,9 +4684,12 @@ void GameScreen::renderNameplates(game::GameHandler& gameHandler) {
         glm::vec3 ndc = glm::vec3(clipPos) / clipPos.w;
         if (ndc.x < -1.2f || ndc.x > 1.2f || ndc.y < -1.2f || ndc.y > 1.2f) continue;
 
-        // NDC → screen pixels (Y axis inverted)
+        // NDC → screen pixels.
+        // The camera bakes the Vulkan Y-flip into the projection matrix, so
+        // NDC y = -1 is the top of the screen and y = 1 is the bottom.
+        // Map directly: sy = (ndc.y + 1) / 2 * screenH  (no extra inversion).
         float sx = (ndc.x * 0.5f + 0.5f) * screenW;
-        float sy = (1.0f - (ndc.y * 0.5f + 0.5f)) * screenH;
+        float sy = (ndc.y * 0.5f + 0.5f) * screenH;
 
         // Fade out in the last 5 units of range
         float alpha = dist < 35.0f ? 1.0f : 1.0f - (dist - 35.0f) / 5.0f;