Add inline validation for group name on edit page

What does this MR do and why?

Follow-up to !239243 (merged) that extends the same inline group-name validation to the group general settings (edit) page (/groups/<group>/-/edit → General → Naming).

Because the edit page is a server-rendered HAML form (not the Vue-based create form), this MR adds a small vanilla-JS validator (group_name_validation.js) that reuses checkGroupNameRules from !239243 (merged) and wires it up via the edit-page entry point.

References

Relates to #597214 (closed)

Depends on: !239243 (merged) (this MR targets that branch; retarget to master after !239243 (merged) merges).

Screenshots or screen recordings

How to set up and validate locally

1. Open /groups/<your-group>/-/edit → General → Naming, visibility in your browser.
2. Verify error states:
   1. Clear Group name and submit → expect Group name is required. inline, form does not submit.
   2. Type -foo → expect inline format error.
   3. Type foo$bar → expect inline format error.
3. Verify valid input shows no error and allows saving:
   1. Type My Group and save → expect successfully updated flash.
   2. Type 🚀 Rockets (emoji start) and save.
   3. Type _internal and save.
4. Verify recovery:
   1. Type -bad, then clear the field → expect error disappears (and aria-invalid resets).
   2. Type -bad, then fix to bad → expect error disappears.
5. Verify accessibility:
   1. With the field invalid, screen-reader users should hear the error text (linked via aria-describedby).
6. Verify no regressions:
   1. Other settings on the page (description, visibility, etc.) save normally.

MR acceptance checklist

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