Add a country field for people and localize the calendar to the active language

[NicoPennec]

Problem

• Kitsu couldn't record where a team member is based, information the studio needs to estimate its per-country carbon footprint.
• People had no way to set their own country from their profile.
• The user calendar was always shown in English, ignoring the chosen interface language.
• The People CSV import only recognized a few of the fields a person actually has, so bulk edits couldn't cover the rest.

Solution

• Add a Country field to people, shown in the people list and editable from the edit form (hidden for bots and clients).
• Let users choose their own country from their profile.
• Show country names in the active interface language, falling back to the raw code when no translation is available.
• Make the user calendar follow the active language and switch live when the language changes.
• Recognize the remaining person fields (Departments, Country, Position, Seniority, Daily rate) as People CSV import columns.

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PR linked to cgwire/zou#1100