[YatesMold]

Closes #28

Doxygen was already set up on main through the CI work in #33, so this PR is the documentation part of the issue.

What changed

• Doxyfile: PYTHON_DOCSTRING = NO (one line). With YES, Doxygen shows docstrings as plain text and ignores @brief, @param and @return. With NO, it reads them as Doxygen comments, so the generated pages get file descriptions, parameter tables and return values.
• Docstrings in all 11 files under src/unidesk are now in Doxygen style (@file, @brief, @param, @return), one commit per file. No code changes.
• The <name> and <filename> placeholders in text_data.py and loader.py were rewritten, because Doxygen read them as HTML tags and warned.

Checked

• doxygen Doxyfile gives no warnings.
• pylint src/unidesk is still clean (0 messages before and after).

Left out on purpose

• Private methods (EXTRACT_PRIVATE = NO), functions nested inside other functions, empty __init__.py files and setup.py (not in INPUT).

Question

EXTRACT_ALL is still YES, so Doxygen does not warn about undocumented code, and a "warnings must not increase" check would have almost nothing to catch. With it set to NO, Doxygen reports 34 warnings right now: 20 for module-level constants (UI, PAGES, CONFIG_PATH and similar) and 14 for private methods and attributes of UniOSWelcome in main_window.py. Two of those (_toggle_autostart and _show_academic_config) are Doxygen reading the .connect(...) lines as variables, so docstrings cannot fix them.

I left EXTRACT_ALL on so this PR stays about the docstrings. Should I document the constants and private helpers and switch it in a follow-up, or leave that?