/explore says once when a `kind:` or `sort:` word is not one it knows, and names the ones it takes #7595

Today /explore?q=sort:bogus silently ignores the word (src/actions/explore.ts:87) and echoes it back in every filter link, so a person never learns why the order did not change.

Done when

• [ ] parseExplore (or its equivalent) returns the unknown kind:/sort: words alongside the query, as plain data
• [ ] The explore page shows one quiet line under the search box: sort:bogus is not a sort — use, forks, ships, fresh (the list from the same constant the parser reads), and the filter links drop the unknown word
• [ ] /api/v1/explore (and MCP, if it reads the same parser) answers the same note in a field, not an error
• [ ] Tests: an unknown sort and an unknown kind each yield the note; a known one yields none; the note is escaped (sort:<b> renders as text)
• [ ] bun scripts/design-lint.ts passes

Files: src/actions/explore.ts, src/web/studio/explore.ts, test/explore-unknown-words.test.ts (new)

Risks. Turning a forgiving search into an error; it stays a note and results still show.

Suggested brief: scout (a person assigns).