refactor(core/rendering): FONT_SIZE_PX compartit a hud_constants.hpp (HC-05)

Notifier::TEXT_SIZE i el TEXT_SIZE del namespace anònim de render_info
declaraven, els dos, "8" com l'alçada del glif de 8bithud. Ara
Rendering::Hud::FONT_SIZE_PX (a core/rendering/hud_constants.hpp) és
l'única font de veritat; Notifier i RenderInfo l'inclouen.

HC-04 (moure la resta de constants HUD a YAML) es marca DEFERRED al
document: és una feature de runtime-config, no pura neteja.

Build + smoke 5s xvfb OK (exit 124).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

source/core/rendering/render_info.cpp

@@ -6,6 +6,7 @@
 #include <cstdio>
 #include <string>
 
+#include "core/rendering/hud_constants.hpp"
 #include "core/rendering/screen.hpp"
 #include "core/rendering/text.hpp"
 #include "core/resources/resource_cache.hpp"
@@ -14,7 +15,7 @@
 
 namespace {
 
-    constexpr int TEXT_SIZE = 8;
+    constexpr int TEXT_SIZE = Rendering::Hud::FONT_SIZE_PX;
     constexpr int PADDING_V = (RenderInfo::HEIGHT - TEXT_SIZE) / 2;
 
     // Llindar per saltar el dibuixat d'un segment quasi totalment transparent.