chore(perf): add live CPU profiling scripts

Standalone Playwright/CDP profilers used to find the main-thread bottlenecks:
- profile-live.mjs: cold-load CPU profile + long-task report against a URL.
- diagnose-feed.mjs: dumps feed DOM/app-state/console to explain empty feeds.
- profile-seeded.mjs: seeds an in-process mock relay, drives login/tab-switch/
  modal-open in test mode, and attributes secp256k1 self-time to its nearest
  app-level caller.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

scripts/perf/diagnose-feed.mjs

@@ -0,0 +1,44 @@
+import { chromium } from "playwright";
+
+const URL = process.argv[2] || "http://localhost:3000/";
+const WAIT_MS = Number(process.env.WAIT_MS || 20000);
+
+const browser = await chromium.launch({ headless: true });
+const page = await browser.newPage({ viewport: { width: 1280, height: 900 } });
+
+const logs = [];
+page.on("console", (m) => logs.push(`[${m.type()}] ${m.text()}`.slice(0, 300)));
+page.on("pageerror", (e) => logs.push(`[pageerror] ${String(e).split("\n")[0]}`));
+
+await page.goto(URL, { waitUntil: "domcontentloaded" });
+await page.waitForTimeout(WAIT_MS);
+
+const state = await page.evaluate(async () => {
+  const out = {};
+  try {
+    const t = window.__bitvidTest__;
+    out.harness = !!t;
+    if (t && typeof t.getAppState === "function") {
+      out.appState = await t.getAppState();
+    }
+  } catch (e) {
+    out.harnessError = String(e).split("\n")[0];
+  }
+  const list = document.querySelector('[data-testid="video-list"]');
+  out.videoListFound = !!list;
+  out.videoListChildCount = list ? list.children.length : null;
+  out.videoListText = list ? (list.textContent || "").trim().slice(0, 200) : null;
+  out.cardsByDataVideoId = document.querySelectorAll("[data-video-id]").length;
+  // any visible error/lockdown banners
+  out.bodyTextSample = (document.body.textContent || "").replace(/\s+/g, " ").trim().slice(0, 400);
+  return out;
+});
+
+console.log("\n===== FEED DIAGNOSIS =====");
+console.log(JSON.stringify(state, null, 2));
+console.log("\n===== CONSOLE (errors/warnings first 40) =====");
+for (const l of logs.filter((l) => /error|warn|fail|lockdown|relay|reject/i.test(l)).slice(0, 40)) {
+  console.log(l);
+}
+console.log(`\n(total console lines: ${logs.length})`);
+await browser.close();