MCP explore answers how many results a filter leaves, in the page's own sentence #11496

Intent: the explorer page says how many results a filter leaves and offers 'clear filters'; a harness asking the same gets the same.

Done:

• [ ] explore answers total and line (the page's sentence) and, when a filter is set, clear (the call that drops it)
• [ ] Sentence comes from the function the page uses; one place for the words
• [ ] A test covers a filter with results, with none, and with no filter; fails without the change
• [ ] bun test test/mcp-size.test.ts passes

Files: src/http/mcp/tools/explore.ts, test/mcp-explore-count.test.ts

Risks: overlaps the cards issue on explore.ts; build after it if both are open. Suggested: scout.