Peers date consistency fixes as follow up to PR384

[jonasbardino]

Force Show Peers date to display on same format as the date picker by wrapping it in a dummy input field without border.
Limit date picker UI and backend accepted date range to dates between 7 days from today and ~10 years in the future, with fallback to default 365 days if an invalid value is given. Highlight the fallback in output. The end date value is automatically interpreted as until midnight and the defaults are now read from mig/shared/defaults.py both for UI and backend.

[jonasbardino]

Lint errors are from old unrelated code and should be fixed by PR #386 .

[jonasbardino]

Verified on one of our test deployments.

[aputtu]

Tested with focus on adherence to:

1. Naming convention, changing "Expire" to "End Date" in Show Peers tab. This allows us to distinguish account expiry in relation to automated renewals from the end date that peer contact sets as a hard limit to access
2. Ability to set minimum and maximum end dates; ie. respectively 7 days and 10 years from current date.

Tested with Ubuntu 24.04 (Wayland, dark mode).

Naming in Show Peers needs adjustment ⛔
Needs adjustment on tabs: Show Peers, Enter Peers, and Import Peers (Not tested Requested Peers)

Minimum end date should be current date + 7 days ✔️

Maximum end date should be current date + 10 years ✔️

[jonasbardino]

Thanks for thorough testing and review 👍
This PR is against the main branch so it doesn't have the 'Expire' -> 'End date' naming fixes of PR #384, yet, but once merged we will get both the naming and the consistency fixes in the main branch.