docs: update copilot instructions for clarity and conciseness

Signed-off-by: szdytom <szdytom@qq.com>

.github/copilot-instructions.md

@@ -1,2 +1,3 @@
-+ Always use English for code comments and documents.
-+ Don't create getters or setters if they are not necessary.
++ English-only comments and documentations
++ Check dev.md first
++ Avoid redundant getters/setters

tilemap/docs/api.md

@@ -166,3 +166,5 @@ istd::BiomeType biome = chunk.get_biome(sub_pos);
 const auto& props = istd::get_biome_properties(biome);
 std::cout << "Biome: " << props.name << std::endl;
 ```
+
+<!-- DO NOT LIST INTERNAL API HERE -->