feat: support freshness parameter for Perplexity web_search provider (#15343)

Merged via /review-pr -> /prepare-pr -> /merge-pr.

Prepared head SHA: 01aba2bfba
Co-authored-by: echoVic <16428813+echoVic@users.noreply.github.com>
Co-authored-by: sebslight <19554889+sebslight@users.noreply.github.com>
Reviewed-by: @sebslight

src/agents/tools/web-search.e2e.test.ts

@@ -31,6 +31,7 @@ const {
   isDirectPerplexityBaseUrl,
   resolvePerplexityRequestModel,
   normalizeFreshness,
+  freshnessToPerplexityRecency,
   resolveGrokApiKey,
   resolveGrokModel,
   resolveGrokInlineCitations,
@@ -128,6 +129,24 @@ describe("web_search freshness normalization", () => {
   });
 });
 
+describe("freshnessToPerplexityRecency", () => {
+  it("maps Brave shortcuts to Perplexity recency values", () => {
+    expect(freshnessToPerplexityRecency("pd")).toBe("day");
+    expect(freshnessToPerplexityRecency("pw")).toBe("week");
+    expect(freshnessToPerplexityRecency("pm")).toBe("month");
+    expect(freshnessToPerplexityRecency("py")).toBe("year");
+  });
+
+  it("returns undefined for date ranges (not supported by Perplexity)", () => {
+    expect(freshnessToPerplexityRecency("2024-01-01to2024-01-31")).toBeUndefined();
+  });
+
+  it("returns undefined for undefined/empty input", () => {
+    expect(freshnessToPerplexityRecency(undefined)).toBeUndefined();
+    expect(freshnessToPerplexityRecency("")).toBeUndefined();
+  });
+});
+
 describe("web_search grok config resolution", () => {
   it("uses config apiKey when provided", () => {
     expect(resolveGrokApiKey({ apiKey: "xai-test-key" })).toBe("xai-test-key");