Show term end dates and time remaining for representatives

[k7lim]

Problem

Users should be able to tell how long each representative is expected to remain in office. The UI currently does not expose term end dates or time remaining.

Desired behavior

• Show term end date and a simple time-remaining display when reliable source data supports it.
• Distinguish normal election cycles, appointment periods, vacancies, and offices with unusual term rules.
• Avoid guessing when term data is unavailable, stale, or ambiguous.
• Include source/last-updated context where possible.
• Add tests for available, unavailable, and ambiguous term data cases.

Notes

This lines up with docs/roadmap.md under Terms. Implementation may require expanding the representative schema and provider mapping before updating the UI.