feat(linkedin-search): add --jobage-minutes for sub-day freshness windows (#302)

jobageToTPR() only emits whole-day f_TPR windows, so a search can't be
restricted to postings from the last N minutes. LinkedIn's f_TPR filters
server-side down to one-second granularity (confirmed empirically), so
this is a pure window-construction change via a new minutesToTPR()
helper - no HTML parsing changes needed.

--jobage-minutes and --jobage both express a freshness window; passing
both is rejected with CONFLICTING_AGE_FLAGS rather than one silently
overriding the other.

.agents/skills/linkedin-search/cli/tests/search.test.ts

@@ -39,4 +39,23 @@ describe("runSearch", () => {
     expect(code).toBe(0);
     expect(JSON.parse(stdout).results).toHaveLength(0);
   });
+
+  test("--jobage-minutes 30 constructs f_TPR=r1800 in the request URL", async () => {
+    let capturedUrl = "";
+    globalThis.fetch = (async (input: RequestInfo | URL) => {
+      capturedUrl = typeof input === "string" ? input : input.toString();
+      return new Response("");
+    }) as typeof fetch;
+
+    const code = await runSearch({
+      location: "Remote",
+      jobage: 9999,
+      jobageMinutes: 30,
+      page: 1,
+      format: "json",
+    });
+
+    expect(code).toBe(0);
+    expect(capturedUrl).toContain("f_TPR=r1800");
+  });
 });