feat: Display copyright term descriptions on term pages

Closes T405598

Summary

Adds Wikidata description display to term pages to provide context about copyright terms, matching the descriptive style of the countries page.

Changes

• Modified term_page() route handler in app.py to pass term description to template
• Added description paragraph in term.html between page title and country grid
• Styled description consistently with countries page using <p class="p-1"> class

Screenshots

Before

50 and 70 years pma:

After

50 and 70 years pma:

Test plan

• Visit any term page (e.g., /term/Q47246828 for "70 years pma")
• Verify term description from Wikidata displays as a paragraph between the page title and country grid
• Verify styling matches the countries page description text
• Test with multiple term pages to ensure descriptions display correctly