The waves pages mark no repository tab as Files, and an empty waves page says what a wave is and how to cut the first #6149

Seen on 2026-10-26: /trevato/forge/waves marks the Files tab as current, because src/web/pages/waves.ts passes "code" to scopeHeader. Its empty state says only This repository has no waves/ directory., which tells a reader nothing about what a wave is.

Done when:

• [ ] Neither /:owner/:name/waves nor /waves/:version marks a tab as current, or both mark the tab that docs/design names for story pages. A test asserts there is no aria-current on Files.
• [ ] The empty state says in one sentence what a wave is. For an admin of the repository, it carries the existing Cut a wave action (POST /:owner/:name/settings/wave). A reader sees no button.
• [ ] Tests cover the admin and the reader.
• [ ] Run bun scripts/design-lint.ts.

Files: src/web/pages/waves.ts, test/waves-page.test.ts.