Move hardcoded text into JSON resources

[YatesMold]

Summary

Moves UniDesk's user-facing text out of Python and into JSON files under
src/unidesk/resources/text_data/, loaded through a small text_data.py
module via importlib.resources. This is a pure data move: identical
behavior and rendering before and after, verified mechanically (see below).

Closes #19

What moved

File	Contents
navigation.json	nav button labels and footer links
pages.json	the five prose page bodies, in display order
faq.json	FAQ as structured {question, answer} entries
links.json	the Links page (7 entries)
credits.json	contributors
ui_strings.json	about 20 interface strings (buttons, titles, hero text, academic-profile labels)

pages.py, credits.py, and links.py are deleted. setup.py gained a
package_data entry so the JSON actually ships in the built wheel/.deb;
previously nothing did, since package_data was never declared at all.

The FAQ is the one place the shape of the data changed: it's now structured
objects instead of one flattened string. The loader flattens it back to the
exact original string at load time, so the widget code that renders it was
never touched. The round-trip was verified programmatically, not just by eye.

What did not move

• UNIVERSITIES in academic_institutions.py: stays in Python. Its file
  comment states it must stay in sync with UniBackpack's hardcoded C++ values.
• The app icon: stays at the repo-root resources/. Moving it into the
  package would break PKGBUILD's install step and main.py's existing
  fallback path.

[TolisSth]

Alright, good PR in general. A few things to check:

• This will be need to go to JSON too, because we are not going for UniBackpack to better the quality of UniDesk.

  UNIVERSITIES = {
      "Aristotle University of Thessaloniki": ["Informatics", "Physics"],
      "University of Western Macedonia": ["Informatics", "Mechanical Engineering"],
      "University of Macedonia": ["Applied Informatics", "Economics"],
  }

  Also, UniNews which is being refactored right now is going to need that more than UniBackpack so let's do that.
• If you want to have a module level src/unidesk/resources let's rename resources to something like assets.