Document the libakgl API with Doxygen

Add file, structure, global, and function documentation across all libakgl-owned headers and sources, including parameter contracts and likely AKERR/AKGL_ERR exceptions. Add a strict Doxyfile and build the generated API documentation in Gitea CI with warnings treated as failures.

Co-authored-by: Codex (GPT-5) <noreply@openai.com>

include/akgl/staticstring.h

@@ -1,3 +1,8 @@
+/**
+ * @file staticstring.h
+ * @brief Declares the public staticstring API.
+ */
+
 #ifndef _STRING_H_
 #define _STRING_H_
 
@@ -7,12 +12,28 @@
 
 #define AKGL_MAX_STRING_LENGTH            PATH_MAX
 
+/** @brief Provides a fixed-capacity, heap-managed string buffer. */
 typedef struct
 {
   int refcount;
   char data[AKGL_MAX_STRING_LENGTH];
 } akgl_String;
 
+/**
+ * @brief String initialize.
+ * @param obj Object to initialize, inspect, or modify.
+ * @param init Optional initial string contents; `NULL` clears the buffer.
+ * @return `NULL` on success, otherwise an error context owned by the caller.
+ * @throws AKERR_NULLPOINTER When the corresponding validation or operation fails.
+ */
 akerr_ErrorContext AKERR_NOIGNORE *akgl_string_initialize(akgl_String *obj, char *init);
+/**
+ * @brief String copy.
+ * @param src Source value to copy or inspect.
+ * @param dst Output destination populated by the function.
+ * @param count Maximum number of elements or bytes to process; zero selects the default.
+ * @return `NULL` on success, otherwise an error context owned by the caller.
+ * @throws AKERR_NULLPOINTER When the corresponding validation or operation fails.
+ */
 akerr_ErrorContext AKERR_NOIGNORE *akgl_string_copy(akgl_String *src, akgl_String *dst, int count);
 #endif //_STRING_H_