docs: surface Kijiji AND-matching behavior in tool, API, and MCP responses

Kijiji zero-result queries (e.g. 'macbook air m1 apple silicon') are
confusing because the failure mode is non-obvious. Surface the root
cause everywhere the caller can see it:
- MCP tool description warns about AND-matching and gives a concrete
  before/after example
- API 404 body includes the actionable hint via emptySearchResponse(hint)
- Core scraper logs the built URL and tip on page-1 zero results
- MCP handler unwraps the API message field so the hint reaches the LLM

packages/mcp-server/src/protocol/handler.ts

@@ -138,7 +138,14 @@ export async function handleMcpRequest(req: Request): Promise<Response> {
             logger.error(
               `[MCP] Kijiji API error ${response.status}: ${errorText}`,
             );
-            throw new Error(`API returned ${response.status}: ${errorText}`);
+            let errorMessage = `API returned ${response.status}: ${errorText}`;
+            try {
+              const errorJson = JSON.parse(errorText) as { message?: string };
+              if (errorJson.message) errorMessage = errorJson.message;
+            } catch {
+              // not JSON — use raw text
+            }
+            throw new Error(errorMessage);
           }
           result = await response.json();
           logger.log(