fix(admins): limit server access to two columns

[rumblefrog]

Description

• cap the Add Admin server-access grid at two desktop columns and one mobile column
• request full server hostnames and wrap them instead of truncating distinguishing suffixes
• add desktop, mobile, overflow, and hydration regression coverage
• update the hydration contract documentation

Motivation and Context

Closes #1491.

The prior auto-fill layout could place three or more servers on one row and requested hostnames with a 40-character cap. Similar servers could therefore become indistinguishable.

How Has This Been Tested?

• ./sbpp.sh phpstan
• ./sbpp.sh test (1202 tests, 4943 assertions)
• ./sbpp.sh ts-check
• ./sbpp.sh composer api-contract
• CI=1 ./sbpp.sh e2e (390 passed, 322 skipped)
• focused PHPUnit and Playwright checks after rebasing onto current origin/main
• separate adversarial review, with all findings resolved and a clean final pass

Screenshots (if appropriate):

Not included. The Playwright regression covers desktop and 390px layouts, full-hostname wrapping, tile placement, and horizontal overflow.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.