Replace credential with secret in user-visible text

Directory's tab and button now say Secrets / "Add secret" (task 11023), but the pages behind them still say "credential": - The create page opened by "Add secret" is titled "New credential", with "New credential" in its breadcrumb (`apps/web/src/pages/credentials/CredentialEditPage.tsx`). Name it "New secret". - The empty Secrets list reads "No credentials yet" (`pages/credentials/Credentials.tsx`). Make it "No secrets yet". - Secrets page filters and notices still mention credentials. Use "secret" wherever a person reads it; code identifiers and addresses (`/credentials`) stay. - Reader docs (`apps/docs/content/console-reference/directory/credentials.md`, `using-jaah/credentials/`) follow the same words. Out of scope: renaming code identifiers, routes, API fields or permission keys (`credentials:*`). Done means: on the live stack, Directory › Secrets › Add secret shows "New secret" in the title and breadcrumb; an empty list says "No secrets yet"; `grep -rn "credential" apps/web/src/pages/credentials --include=*.tsx` finds no user-visible string, only identifiers and comments; `./dc check quick` is green.

Secrets pages, filters, bulk/tree/notices and reader docs now say "secret" ("New secret", "No secrets yet"); stored-values filter is "Values". Quick gate + 862 tests green; visual check confirmed. PR #7253 queued. Accounts pages keep "credential" (login tokens), so the grep oracle is too broad. Memory: none applied.