Frontend: More dayjs -> Temporal migration

[tristanlabelle]

• Migrate misc code still using dayjs to Temporal.
• Abstract dayjs' "humanize" api behind localizeDuration for consistency and so we can switch to browser APIs in the future.
• Extract spreading a duration's units into approximate date units and back (approxTimeDuration + approxDateDuration)
• Add more tests

There are still some public trip-related code using dayjs but I don't know how to test that so I didn't touch it.

Testing

Compared vercel preview and next: host requests, last active, local time, upcoming trips+stays on dashboard. Saw no difference.

Web frontend checklist

• There are no console warnings when running the app
• Added tests where relevant
• Clicked around my changes running locally and it works
• Checked Desktop, Mobile and Tablet screen sizes

For maintainers

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

[CouchersBot]

Mobile

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Deep links

iOS

couchers-devtool://expo-development-client/?url=https%3A%2F%2Fb51f5c7e--ota.preview.couchershq.org%2Fios%2Fmanifest

Android

couchers-devtool://expo-development-client/?url=https%3A%2F%2Fb51f5c7e--ota.preview.couchershq.org%2Fandroid%2Fmanifest

Web (Vercel)

View the Vercel web preview for this branch.

Backend

Schema	Schema diff	Sample emails

Other

Protos	Backend coverage	Web coverage

[nabramow]

Just one nit with the comment, otherwise everything seems to work as before!

[github-actions]

📝 Release Notes

This PR does not need to be included in release notes.

Reason: This PR is primarily an internal frontend refactor migrating date handling from dayjs to Temporal, with added abstractions and tests. The author explicitly noted that tested user flows showed no visible difference, and the changes do not introduce a new feature or a clearly noticeable bug fix for end users. While it may improve code consistency and future maintainability, it does not rise to the level of major technical infrastructure work that should appear in release notes.

🤖 Bot Debug Information

Model: couchers.openai.gpt-5.4
Decision: exclude
Reasoning: This PR is primarily an internal frontend refactor migrating date handling from dayjs to Temporal, with added abstractions and tests. The author explicitly noted that tested user flows showed no visible difference, and the changes do not introduce a new feature or a clearly noticeable bug fix for end users. While it may improve code consistency and future maintainability, it does not rise to the level of major technical infrastructure work that should appear in release notes.