style: Add 3-line descriptive headers to all source files

This commit applies a new project-wide rule that every source file must begin with a concise 3-line comment header describing its purpose.

- Updated CONTRIBUTING.md with the new rule.

- Applied headers to all .cc and .h files in src/ and tools/.

- Fixed various minor compilation errors and missing includes discovered during the header update process.

1 files changed, 10 insertions, 7 deletions

diff --git a/tools/asset_packer.cc b/tools/asset_packer.cc
index a67ddcc..8696646 100644
--- a/tools/asset_packer.cc
+++ b/tools/asset_packer.cc
@@ -1,3 +1,7 @@
+// This file is part of the 64k demo project.
+// It implements the asset packer tool for demoscene resource management.
+// Converts external files into embedded C++ byte arrays.
+
 #include <fstream>
 #include <iostream>
 #include <map>
@@ -39,8 +43,8 @@ int main(int argc, char *argv[]) {
 
   // Generate assets.h
   assets_h_file << "#pragma once\n";
-  assets_h_file << "#include <cstdint>\n";
-  assets_h_file << "#include <cstddef>\n\n";
+  assets_h_file << "#include <cstddef>\n";
+  assets_h_file << "#include <cstdint>\n\n";
   assets_h_file << "enum class AssetId : uint16_t {\n";
 
   // Generate assets_data.cc header
@@ -109,8 +113,8 @@ int main(int argc, char *argv[]) {
                           << (i == buffer.size() - 1 ? "" : ", ");
     }
     assets_data_cc_file << "\n};\n";
-    assets_data_cc_file << "const size_t ASSET_SIZE_" << asset_name << " = "
-                        << buffer.size() << ";\n\n";
+    assets_data_cc_file << "const size_t ASSET_SIZE_" << asset_name
+                        << " = " << buffer.size() << ";\n\n";
 
     asset_id_counter++;
   }
@@ -120,9 +124,8 @@ int main(int argc, char *argv[]) {
   // Generate GetAsset function declaration in assets.h
   assets_h_file << "const uint8_t *GetAsset(AssetId asset_id, size_t *out_size "
                    "= nullptr);\n";
-  assets_h_file
-      << "void DropAsset(AssetId asset_id, const uint8_t *asset); // For lazy "
-         "decompression scaffolding\n";
+  assets_h_file << "void DropAsset(AssetId asset_id, const uint8_t *asset); // "
+                   "For lazy decompression scaffolding\n";
   assets_h_file.close();
 
   // Generate GetAsset function implementation in assets_data.cc