Backend/requests: More useful date formats

[tristanlabelle]

#8574 added support for localized date format variants. We can use it with requests to make them more useful: we don't need to show the year since requests are within 365 days (and typically within a month), and we can add the day of the week since that's useful info (hosting weekend vs day of week).

Updates tests accordingly. Which makes me think we should rather mock the system clock: #8854

Testing

After this change:

Before:

Backend checklist

• Added tests for any new code or added a regression test if fixing a bug
• Run the backend locally and it works
• Added migrations if there are any database changes, rebased onto develop if necessary for linear migration history

For maintainers

• Maintainers can push commits to my branch
• Maintainers can merge this PR for me

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Project	Deployment	Actions	Updated (UTC)
couchers	Ready	Preview	May 29, 2026 7:05pm

[github-actions]

📝 Release Notes

This PR should be included in the release notes.

Suggested release note:

Improved host request emails to show clearer dates with the day of the week and without the unnecessary year

🤖 Bot Debug Information

Model: couchers.openai.gpt-5.4
Decision: include
Reasoning: This is a small but noticeable user-facing improvement: host request emails now show clearer dates by including the day of the week and omitting the unnecessary year, which makes request timing easier to understand at a glance.