fix: add automatic date/time format option for locale-native defaults

[Kameti77]

This PR adds an Automatic option to both the date and time format pickers in Language settings. Previously, the only choices were fixed presets (DD/MM/YYYY, MM/DD/YYYY, YYYY-MM-DD for date and HH:mm, h:mm A for time). Many locales use formats that don't match any of these. For example, German uses DD.MM.YYYY, Spanish uses H:mm, and Indonesian uses HH.mm, so users on those locales had no option that correctly reflected their locale's native format, and there was no way to revert to the locale default once an override had been picked.

The Automatic option uses the locale's native dayjs format tokens (L for date, LT for time), so it always displays the correct format for whatever language is selected. Switching languages updates the Automatic preview immediately. Explicit overrides are preserved across language switches and can be reverted to Automatic at any time.

Changes made:

• Language.tsx — Added Automatic as the first option in both pickers. The preview is computed via createMemo tracking a new nativeLocaleFormats signal so it updates reactively when the locale changes. Selecting Automatic calls clearDateFormat()/clearTimeFormat() on the store.
• dayjs.tsx — Added a nativeLocaleFormats signal that captures the locale's original L and LT formats before any user overrides are applied, so the Automatic preview is never affected by a previously picked override.
• Locale.ts — Added a public getOptions() accessor (the existing get() is protected). Fixed clearDateFormat() and clearTimeFormat() to call loadTimeLocale() directly so the locale reloads even when the language itself hasn't changed.
• Time.tsx — Changed the date format case to use dayjs's L token (locale-aware) instead of the hardcoded DD/MM/YYYY. Added a separate dateNormal case that keeps the hardcoded DD/MM/YYYY for the Traditional option preview. Added createEffect so the component updates immediately when the locale signal changes rather than waiting for the next setInterval tick.

Fixes #629

How was this PR tested?

• Switched to German — Date format shows "Automatic" with preview DD.MM.YYYY (dots)
• Switched to Spanish — Time format shows "Automatic" with preview H:mm (no AM/PM, no leading zero)
• Switched to Azerbaijani — Time format shows "Automatic" with correct 24-hour format
• Switched to English (Traditional) — Automatic date preview shows DD/MM/YYYY, time shows h:mm A
• Switched to English (Simplified) — Automatic date preview shows MM/DD/YYYY
• Picked an explicit override (DD/MM/YYYY), then switched languages — override was preserved, did not reset
• Selected Automatic after an explicit override — preview reverted to locale-native format immediately
• Refreshed the page with an explicit override — override persisted correctly
• Refreshed the page with Automatic selected — still showed Automatic with correct locale preview
• Verified Traditional (DD/MM/YYYY), American (MM/DD/YYYY), and ISO Standard previews always show their fixed formats regardless of locale

Screenshots & Screencasts (if appropriate)

Checklist:

• [x ] I have carefully read the contributing guidelines
• I have performed a self-review of my own code
• [x ] I have made corresponding changes to the documentation if applicable
• I have no unrelated changes in the PR
• I have confirmed that any new dependencies are strictly necessary
• I have written tests for new code (if applicable)
• I have followed naming conventions/patterns in the surrounding code

Please declare, if any, LLM usage involved in creating this PR

I used Claude Code (Anthropic) as a pair programming assistant throughout this PR. It helped me navigate the codebase, understand the Solid.js reactivity model, and reason through the timing issues with async locale loading. All code was reviewed and understood before committing.

[Kameti77]

Hi @stoatchat/for-web-maintainers, this is my first contribution. I've fixed #629 by adding an Automatic option to the date/time format pickers so locales like German and Spanish correctly show their native formats. Would appreciate a review when you have time! Looking forward to your feedback.