The Secrets card speaks the home page's language, at the forge, an organization and a repository #9718

For: the card that holds an operator's own credentials is the next page in the design pass that #9706–#9714 carry. One card is drawn in three places, so one change fixes all three.

Done looks like:

• [x] The Secrets card (src/web/pages/secrets.ts) follows the opening principles of docs/DESIGN.md: it uses space where a border or box does no work, and its rows and its set form use the home page's type.
• [x] Nothing is lost: values can only be written, never shown; each row still shows its name, when it was set and when it was last opened; setting and removing still work as plain form posts with the same-origin check.
• [x] The card looks the same at the forge, under an organization and on a repository. A test renders all three and finds the same class names.
• [x] bun scripts/design-lint.ts passes, and so do test/secrets-*.test.ts.

Files: src/web/pages/secrets.ts, plus its area doc under docs/design/areas/ if a class is added. Risks: never echo a value into the page, even in an error message after a failed post. Keep the timing tests within budget.

Reviewed pull #9723 at its head: ticked The Secrets card (src/web/pages/secrets.ts) follows the opening principles of docs/DESIGN.md: it uses space where a border or box does no work, and its rows and its set form use the home page's type.; Nothing is lost: values can only be written, never shown; each row still shows its name, when it was set and when it was last opened; setting and removing still work as plain form posts with the same-origin check.; The card looks the same at the forge, under an organization and on a repository. A test renders all three and finds the same class names.; bun scripts/design-lint.ts passes, and so do test/secrets-*.test.ts..