Resolve UAT Feedback on Settings page

[nathan-stricker]

Summary

Work for #7617 (UAT ticket based on work for #7044)

Changes proposed

• Added error message styling (left aligned red rule on the field)
• Updated "Contact Information" field from H3 to H2 to avoid skipping a heading level
• Added alert banner across top of account page when required fields are empty (with dynamic content based on missing fields)
• Added error icon in the navigation when any of the required fields are empty
• Fixed form labels to be screen reader friendly
• Added help text below form labels for required fields
• Added checkmark icon to save button

Context for reviewers

After work in #7392 for #7044 , received UAT feedback to clean up the page a bit. See feedback here.

See mock here:
https://www.figma.com/design/zPlDWcYM396szw2yL3UXvk/Simpler-Grants-2025?node-id=6166-127247&t=n0FQTNex4mJoGxEJ-1

Validation steps

Note: must disable the userAdminOff feature flag at http://localhost:3000/dev/feature-flags to see changes.

• Initial state: When either first or last name is missing on Settings page:
  • Icon next to "Account" in navigation bar is a red error icon
  • Settings page shows error banner at top of page
• Attempted save: When trying to save profile with an empty first and/or last name:
  • Get an error with a red line to the left of the relevant section
  • Error banner shows dynamic content based on missing field
• Sucessful save: When both first and last name are filled in on Settings page:
  • Success banner displays right after saving, but disappears on page reload
  • Icon next to "Account" in navigation bar is a round profile icon with default color
  • Error banner no longer displays at top of settings page
• Screen reader has no issues on Settings page (used WAVE Chrome browser extension to review)