refactor(render): TextBackend owns its atlas, and staged glyphs carry a rotation basis

src/render/program.cpp

@@ -41,6 +41,8 @@ void TextProgram::set_viewport(Vec2 px) const noexcept { program_.set_uniform("u
 
 void TextProgram::set_px_range(Vec2 px) const noexcept { program_.set_uniform("u_px_range", px); }
 
+void TextProgram::set_glyph_uv(Vec2 uv) const noexcept { program_.set_uniform("u_glyph_uv", uv); }
+
 void TextProgram::set_texture_size(Vec2 texels) const noexcept {
   program_.set_uniform("u_tex_size", texels);
 }