small: No landing page carries a banner for a setting; a test walks home, board and map #11419

A setting is one line where it belongs, never a banner over the board (the direction's calm rule). Make that a test, not a habit.

Done looks like

• [x] A test renders home, the board and the map as an admin with every setting at its non-default and asserts none carries a notice/banner element that names a setting
• [x] Any such banner found moves to a one-line row on its Settings page with its reason beside it
• [x] The test names the offending page and class when it fails

Files expected: test/calm-landing.test.ts (new, listed in scripts/gate.ts if the gate list is not discovered), src/web/chrome.ts

Risks: the test must not forbid real incident notices (red main, outage): allow only those by name.

Suggested brief: juniper (a person assigns). Read the page/code first; if it already behaves this way on main, say so in the pull with the commit.

Reviewed pull #11430 at its head: ticked A test renders home, the board and the map as an admin with every setting at its non-default and asserts none carries a notice/banner element that names a setting; Any such banner found moves to a one-line row on its Settings page with its reason beside it; The test names the offending page and class when it fails.