fix(ui): allow uppercase letters in username on profile settings

[culfin]

Users whose username contains an uppercase letter cannot save their profile at all — not even when they leave the username untouched, because the whole form is validated on submit.

The check in profile settings is the only one of four that rejects uppercase:

where	pattern	uppercase
ui/src/pages/Users/Register/components/SignUpForm/index.tsx	/^[\w.-\s]{2,30}$/	allowed
ui/src/pages/Install/components/FourthStep/index.tsx	/^[\w.-\s]{2,30}$/	allowed
pkg/checker/username.go	^[\w.\- ]{2,30}$	allowed
ui/src/pages/Users/Settings/Profile/index.tsx	/[^a-z0-9\-._]/	rejected

So one can sign up as MaxMustermann, and from then on the profile page is locked. The error message points at the username field without saying why a name the server itself issued is suddenly invalid.

I ran into this migrating a 26-year-old forum to Answer: 3368 of 5479 accounts carry uppercase letters in names that have been in use for two decades.

Proposed Changes

• add the ignore-case flag to the username check in profile settings, bringing it in line with registration, installation and the server
• permits nothing the server would reject; no data or API behaviour changes

An alternative would be to reuse the exact pattern from SignUpForm, but that also allows spaces, which felt like a larger change than this fix needs. Happy to switch if you prefer the patterns to be literally identical.

[robinv8]

@culfin Thanks for the fix — approved. One process note: please retarget this PR to dev instead of main (rebase or merge the latest dev if needed). We land changes on dev first and only promote to main through the normal release process.

[culfin]

Retargeted to dev, along with the rest — thanks for the pointer, and sorry it took a few days to act on it. dev contains everything main has and none of the files these changes touch, so the diffs are unchanged.

While doing that I also consolidated: what were fourteen open pull requests are now seven. Four defects in ui/template/ became #1592, the two halves of the answer-pagination limit became #1593, and the accessibility work that had grown across five PRs is back in two (#1587, #1588). Sorry for the noise on the way there.