fix: datetime displays now respect the app's selected locale

[GiulioSavini]

What

Several components were calling toLocaleString() / toLocaleTimeString() without passing a locale argument, so date displays always followed the OS system locale regardless of what language the user picked inside Arcane.

Fix

Added formatDateTime and formatDateTimeShort utilities to locale.util.ts backed by date-fns, which already picks up the paraglide locale via setDefaultOptions (set when the user changes language). Updated the five affected components:

• event-details-dialog.svelte
• docker-info-dialog.svelte
• job-card.svelte
• vulnerability-scan-item.svelte
• vulnerability-scan-panel.svelte

No behaviour change for users who haven't changed locale. For everyone else, dates now match the language they selected.

Fixes #2349

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Greptile Summary

This PR adds formatDateTime / formatDateTimeShort helpers to locale.util.ts backed by date-fns, then updates five components to use them so that date displays respect the user's in-app locale choice rather than the OS locale.

• In vulnerability-scan-item.svelte the original call was toLocaleTimeString() (time-only), but the replacement is formatDateTime() which outputs the full date + time via the 'PPpp' pattern. This is a visible format change for all users regardless of locale, and may overflow UI elements sized for a time-only string.

Confidence Score: 4/5

Safe to merge after confirming whether the time-only → date+time change in vulnerability-scan-item is intentional.

Four of the five component changes are clean locale-only fixes. The one issue — toLocaleTimeString() replaced by formatDateTime() in vulnerability-scan-item.svelte — changes the displayed information (time-only → date+time) for every user, which is a real behaviour change that should be explicitly confirmed before merging.

frontend/src/lib/components/vulnerability/vulnerability-scan-item.svelte

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This is a comment left during a code review.
Path: frontend/src/lib/components/vulnerability/vulnerability-scan-item.svelte
Line: 87

Comment:
**Unintentional format change: time-only → date+time**

The original call was `parsed.toLocaleTimeString()`, which outputs only the time portion (e.g., `"3:45:22 PM"`). `formatDateTime` uses the `'PPpp'` pattern, which outputs the full date + time (e.g., `"Apr 13, 2026, 3:45:22 PM"`). For every user — including those who never changed the app's locale — `scanStartedLabel` now displays a much longer string, which may overflow any UI elements sized for a time-only value and contradicts the PR's stated goal of no behaviour change for users on the default locale.

If including the date is intentional, that's fine, but it should be called out explicitly. If the intent was purely a locale fix, `formatDateTimeShort` at minimum (or a time-only `date-fns` helper) is the correct replacement.

How can I resolve this? If you propose a fix, please make it concise.

_{Reviews (1): Last reviewed commit: "fix: use app locale for datetime formatt..." | Re-trigger Greptile}

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[kmendell]

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