/explore says once when a `kind:` or `sort:` word is not one it knows, and names the ones it takes #7612

/explore now says once when a kind: or sort: word isn't one it knows, and the results still show. I ran tsc, the explore, TUI-dashboard-explore and mcp-size tests, and design-lint; all pass. I did not run the full suite — the forge's check does that on push.

• Parser: readExploreLine(line) in src/actions/explore.ts returns { query, unknown }. parseExploreQuery still exists and returns just the query. The unknown words are kept as typed and capped at five.
• Note text: exploreNote builds the line, e.g. sort:bogus is not a sort — use score, forks, ships, use, fresh, name. The lists come from the same constants the parser reads. A kind: word gets use app, person, forge.
• Page: the note sits under the search box as a quiet line and is escaped, so sort:<b> renders as text.
• Filter links: an unknown word was previously echoed as plain search text. Now it is dropped, so it no longer appears in the box or the filter links.
• API and MCP: /api/v1/explore and the MCP explore tool add a note field only when there is something to say. The status stays 200 and the tool schema and mcp-size are unchanged.
• Tests: the new test/explore-unknown-words.test.ts covers an unknown sort, an unknown kind, a known word giving no note, the escaping, the filter links, and the API field.
• Two older tests changed: test/explore.test.ts and test/tui-dashboard-explore.test.ts asserted the old behaviour. One expected sort:nonsense to come back as search text. The other expected "Nothing matches" for kind:app sort:nonsense. I updated both to the new behaviour.

Left out: the TUI explore filter drops unknown words the same way (it shares the parser) but shows no note; I didn't add one. A bare kind: with no value is still treated as text, as before.

Closes #7595

/explore now says once when a kind: or sort: word isn't one it knows, and the results still show. I ran tsc, the explore, TUI-dashboard-explore and mcp-size tests, and design-lint; all pass. I did not run the full suite — the forge's check does that on push.

• Parser: readExploreLine(line) in src/actions/explore.ts returns { query, unknown }. parseExploreQuery still exists and returns just the query. The unknown words are kept as typed and capped at five.
• Note text: exploreNote builds the line, e.g. sort:bogus is not a sort — use score, forks, ships, use, fresh, name. The lists come from the same constants the parser reads. A kind: word gets use app, person, forge.
• Page: the note sits under the search box as a quiet line and is escaped, so sort:<b> renders as text.
• Filter links: an unknown word was previously echoed as plain search text. Now it is dropped, so it no longer appears in the box or the filter links.
• API and MCP: /api/v1/explore and the MCP explore tool add a note field only when there is something to say. The status stays 200 and the tool schema and mcp-size are unchanged.
• Tests: the new test/explore-unknown-words.test.ts covers an unknown sort, an unknown kind, a known word giving no note, the escaping, the filter links, and the API field.
• Two older tests changed: test/explore.test.ts and test/tui-dashboard-explore.test.ts asserted the old behaviour. One expected sort:nonsense to come back as search text. The other expected "Nothing matches" for kind:app sort:nonsense. I updated both to the new behaviour.

Left out: the TUI explore filter drops unknown words the same way (it shares the parser) but shows no note; I didn't add one. A bare kind: with no value is still treated as text, as before.

I've addressed all of the review feedback and pushed to the same branch. tsc is clean, and the explore, TUI-dashboard-explore, new-note and mcp-size tests pass. I did not run the full suite — the forge's check does that on push.

• Terminal: the TUI explorer now reads the line with readExploreLine. The note goes on the "Read as:" line after a ·, for example Read as: kind:app · sort:nonsense is not a sort — use score, forks, …. test/tui-dashboard-explore.test.ts has a new test for it. The note shares the line with the "Read as:" text, so a narrow terminal may cut it off rather than wrap it.
• README: one added paragraph in the explorer section. It covers the dropped word, the note after "Read as:", and the note field in /api/v1/explore and the MCP explore tool. That is one paragraph for the three, not one line each.
• MCP: test/explore-unknown-words.test.ts now calls the explore tool over /mcp. It checks that note is returned for sort:bogus and absent for sort:forks.
• Parser: the dangling else if is now } else if, and the over-long comment is re-wrapped.