docs: add meaningful code comments to build_templates.zig

- Added comprehensive module-level documentation explaining architecture
- Added doc comments to all public and key internal functions
- Improved inline comments focusing on 'why' not 'what'
- Updated CLAUDE.md with code comments rule
- Bump version to 0.2.0

build.zig.zon

@@ -1,6 +1,6 @@
 .{
     .name = .pugz,
-    .version = "0.1.11",
+    .version = "0.2.0",
     .fingerprint = 0x822db0790e17621d, // Changing this has security and trust implications.
     .minimum_zig_version = "0.15.2",
     .dependencies = .{},