Implement create custom recommendations

app/api/templates/route.ts

@@ -1,17 +1,31 @@
-import { NextResponse } from "next/server";
+import { NextResponse, type NextRequest } from "next/server";
 import { isDatabaseConfigured } from "../../../lib/server/env";
-import { listRuleTemplatesFromDb } from "../../../lib/server/ruleTemplates";
+import { listRankedRuleTemplatesFromDb } from "../../../lib/server/ruleTemplates";
 import { dbUnavailable } from "../../../lib/server/responses";
+import { parseRequestedFacetsFromSearchParams } from "../../../lib/server/validation/methodFacetsSchemas";
 
 /**
- * Curated rule templates for recommendations (seed via Prisma Studio or a script).
+ * GET /api/templates
+ *
+ * No params → curated ordering (`featured` desc, `sortOrder` asc, `title`
+ * asc). With `facet.<group>=<value>` query params (repeatable per group),
+ * templates are re-ranked by composed-method match count; ties fall back to
+ * the curated order, score-0 templates remain at the end.
+ *
+ * See `docs/guides/template-recommendation-matrix.md` §9.1.
  */
-export async function GET() {
+export async function GET(request: NextRequest) {
   if (!isDatabaseConfigured()) {
     return dbUnavailable();
   }
 
-  const templates = await listRuleTemplatesFromDb();
+  const facets = parseRequestedFacetsFromSearchParams(
+    request.nextUrl.searchParams,
+  );
+  const { templates, scores } = await listRankedRuleTemplatesFromDb(facets);
+  const hasScores = Object.keys(scores).length > 0;
 
-  return NextResponse.json({ templates });
+  return NextResponse.json(
+    hasScores ? { templates, scores } : { templates },
+  );
 }