HUD pass, weapon and trinket rework, and font arrows

HUD:
- Hotbars fit a quarter of the screen, dropping to small then tiny slots
  (thinner outlines when tiny), with cooldown bars matching their size.
- HUD elements are drawn on their own layer and composited at one
  opacity: hotbar slots are see-through until hovered, the rest fade
  while hovered.
- Rival windows fit the right column in at most two rows, shrinking
  icons then font, then dropping icons for name, health and ping bars.
- Tooltips number equipped items' slots and say Recoil for weapons that
  only push back. Previews use arrows, spread uses degrees.
- Crosshair fills in and shakes with charge, and weapons shake after
  firing until their cooldown ends. DPS and speed meters off by default.

Gameplay:
- Dual Wield stacks: each copy fires another recently held weapon from
  a fanned off-hand, at its own level's cut.
- Flamethrower: no slowing, smaller fireball with some recoil, and an
  airblast that knocks others away.
- Iron Weights slam on any landing faster than a plain fall (platforms
  too), stacking radius and damage, and speeding fast falls.
- Stuck arrows are one-way ledges until they fade, matching their
  (slightly larger) hit size. Attacks now collide with slopes.
- Halved Tesla Coil, Recoil Coil, Diazepam, Shock Absorber, Feather and
  screenshake values.

Art and tools:
- Weapon and trinket icons merged into one sheet each (normal, small,
  tiny), cells in catalog order. Grimoire wisps stand upright.
- Fonts gain the degree sign and four arrows, decoded from UTF-8.
- Menu fighter preview walks at quarter speed.
- Unequip from either catalog tab by right click or gamepad.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/effects.h

@@ -49,6 +49,15 @@ struct Flash
     float size = 0;
 };
 
+// A ring swelling out to its radius as it fades, like an airblast.
+struct Ring
+{
+    Color color;
+    Vec2 position;
+    float life = 0;
+    float radius = 0;
+};
+
 // A fading copy of a sprite left behind by something moving fast.
 struct Afterimage
 {
@@ -63,6 +72,7 @@ public:
     void burst(Burst burst, Vec2 position, float angle, Color color);
     void afterimage_spawn(Pose pose);
     void flash_spawn(Vec2 position, float angle, float size, Color color);
+    void ring_spawn(Vec2 position, float radius, Color color);
     void afterimage_draw(Game& game);
     void number_spawn(Vec2 position, int value, int target, Color color);
     void dps_record(int amount);
@@ -80,6 +90,7 @@ private:
     std::vector<Hit> hits;
     std::vector<Particle> particles;
     std::vector<Popup> popups;
+    std::vector<Ring> rings;
     float shake = 0;
     int ticks = 0;
 };