fix: update documentation links in product descriptions

[Kylakauppias]

Summary

Updates the documentation links in src/takrmapi/api/description.py to point to language-specific guide pages instead of the generic docs root.

Changes

Replaces https://docs.pvarki.fi/ with the correct language-specific TAK guide URLs across all three language branches:

• fi → https://docs.pvarki.fi/fi/docs/guides/tak-guide
• sv → https://docs.pvarki.fi/sv/docs/guides/tak-guide
• en → https://docs.pvarki.fi/en/docs/guides/tak-guide

Why

Users were being directed to the documentation root rather than the relevant TAK guide for their language, resulting in a poorer experience when following documentation links from the product UI.