Rearrange connected accounts in stacked layout

[aduth]

🎫 Ticket

Supports LG-13665

🛠 Summary of changes

Updates the layout of the connected accounts page to show the content of individual accounts in a stacking arrangement, with a "Disconnect" button.

This incrementally works toward LG-13665, pending clarification about identities without linked emails.

It also includes a bit of general clean-up:

• Avoid String#html_safe in favor of _html suffix for locale string
• Use semantic HTML markup (headings for each item, <ul> for list of accounts)

📜 Testing Plan

1. Go to http://localhost:3000
2. Sign in
3. Click "Your connected accounts"
4. Observe that accounts are rendered as shown in "After" screenshot

👀 Screenshots

Before	After