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/parsing.test.ts

@@ -1,5 +1,5 @@
 import { describe, test, expect } from "bun:test";
-import { parseJobCards, parseJobDetail, extractDivContent } from "../src/helpers";
+import { parseJobCards, parseJobDetail, extractDivContent, minutesToTPR } from "../src/helpers";
 
 // Minimal search-card markup: parseJobCards splits on the job-posting URN and
 // needs an id, a base-search-card__title, and a full-link. Everything else is
@@ -111,3 +111,16 @@ describe("extractDivContent", () => {
     expect(job.description).toContain("We are hiring!");
   });
 });
+
+describe("minutesToTPR", () => {
+  test("converts minutes to an f_TPR seconds window", () => {
+    expect(minutesToTPR(30)).toBe("r1800");
+    expect(minutesToTPR(1)).toBe("r60");
+    expect(minutesToTPR(1440)).toBe("r86400"); // matches jobageToTPR(1)
+  });
+
+  test("returns null for non-positive input", () => {
+    expect(minutesToTPR(0)).toBeNull();
+    expect(minutesToTPR(-5)).toBeNull();
+  });
+});