merged AI doc, some new pages

doc/pages/code_model.md

@@ -3,6 +3,26 @@
 
 \~english
 
+# Introduction
+
+Code generation helps when you need string representation of entities (classes, enums, etc.) or automated serialization/deserialization of structures and classes. For example, you may need a list of "name" = "value" pairs from an enumeration for a UI, or to traverse nested structures with metadata. You can describe a structure of any complexity, assign field IDs, and get ready-made operators for \a PIBinaryStream with versioning and backward compatibility.
+
+# pip_cmg
+
+PIP provides the \c pip_cmg utility: it takes source files, include paths, and options, and produces a .h/.cpp pair. Depending on options, the output may include: entity metadata; serialization operators; and the ability to get a \a PIVariant for any member by name.
+
+Processing options: \c -s (do not follow #include); \c -I<include_dir> (add include path); \c -D<define> (add macro; \c PICODE is always defined).
+
+Creation options: \c -A (create all); \c -M (metadata); \c -E (enums); \c -S (serialization operators); \c -G (get value by name); \c -o <output_file> (output base name without extension).
+
+# CMake
+
+The \c pip_code_model CMake macro invokes \c pip_cmg and keeps the model up to date. Call format: \c pip_code_model(<out_var> file0 [file1 ...] [OPTIONS ...] [NAME name]). Parameters: \c out_var receives generated file paths; \c file... are sources; \c OPTIONS are passed to \c pip_cmg (e.g. \c "-Es"); \c NAME sets the model file base (default \c "ccm_${PROJECT_NAME}"). The macro adds PIP include paths. Run \c pip_cmg -v for current options.
+
+# Details
+
+Metadata: attach \c PIMETA(...) to types, members or enums; read at runtime via \a PICODEINFO::classes() and \a PICODEINFO::enums(). Serialization: struct-level \c PIMETA(simple-stream) or \c PIMETA(no-stream), or per-member chunk ids (default); see \ref chunk_stream. Add the generated .h/.cpp to your target and \c #include the generated header; metadata loads before \c main().
+
 \~russian
 
 # Введение