Add blood decals, gore, mobile HUD, web start gate + touch/perf tests

Remove tools/fstest.html scratch page used to probe browser
fullscreen/orientation APIs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EznnY8rH2dXhtono1kwsXg

blood_decals.gdshader

@@ -0,0 +1,26 @@
+shader_type spatial;
+// Persistent blood splats, drawn as one MultiMesh of flat quads (see blood_decals.gd).
+// Unshaded and nearest-filtered to sit inside the PS1 look; alpha-blended so overlapping
+// splats pool darker. depth_draw_never + the small normal offset the pool bakes into each
+// transform keep the coplanar floor/wall quads from z-fighting the surface they stain.
+render_mode unshaded, cull_disabled, shadows_disabled, depth_draw_never, blend_mix;
+
+uniform sampler2D atlas : source_color, filter_nearest;
+// Number of splat shapes packed side-by-side in the atlas (one row).
+uniform int cells = 8;
+
+varying flat float v_cell;
+varying flat float v_shade;
+
+void vertex() {
+	// x = which atlas shape this instance uses; y = per-instance brightness (fresh vs old).
+	v_cell  = INSTANCE_CUSTOM.x;
+	v_shade = INSTANCE_CUSTOM.y;
+}
+
+void fragment() {
+	float u = (UV.x + v_cell) / float(cells);
+	vec4 c = texture(atlas, vec2(u, UV.y));
+	ALBEDO = c.rgb * v_shade;
+	ALPHA = c.a;
+}