test: timing budgets + CI hardening (artifact v3 pin, npm cache retry)

Closes three items from the outstanding e2e/CI gap list:

- Timing budgets: timings.measure() only ever recorded durations for the
  (still-unwired) Pushgateway export — nothing failed CI when a step got
  slow. Add e2e/timing-budgets.ts (expectWithinBudget + shared BUDGET_MS
  buckets) and wire it into every measure() call site across the suite.
  Mail-wait steps are deliberately left unbudgeted (external mail-trap
  delivery latency, not a code performance signal).

- actions/upload-artifact@v4 doesn't work against this Gitea/act runner's
  artifact backend — pin to v3 for the e2e failure-report upload.

- Shared act_runner npm cache has corrupted platform-native tarballs before
  (@next/swc-linux-x64-musl) and reds viewer-unit/admin-unit/e2e with no
  product bug involved. All three npm ci steps now retry once after
  `npm cache clean --force` on first failure.

Verified: full local suite green against DEV (37 passed, 6 skipped, no
budget assertion failures) before wiring into CI.

e2e/tests/upload.smoke.spec.ts

@@ -1,6 +1,7 @@
 import { assertPublicHost, interceptNetworkCall, waitForUrlHost } from '@levkin/playkit';
 import path from 'node:path';
 import { test, expect } from '../fixtures';
+import { BUDGET_MS, expectWithinBudget } from '../timing-budgets';
 
 const tinyPng = path.join(__dirname, '../fixtures/tiny.png');
 
@@ -18,6 +19,7 @@ test.describe('upload @smoke', () => {
       await page.goto(`${playkitConfig.baseUrl}/upload`);
       await waitForUrlHost(page, playkitConfig.expectedHost);
     });
+    expectWithinBudget(timings, 'open_upload', BUDGET_MS.uiAction);
 
     expect(new URL(page.url()).pathname).toMatch(/\/upload/);
     await expect(page.getByLabel('Account menu')).toBeVisible({ timeout: 20_000 });
@@ -52,5 +54,7 @@ test.describe('upload @smoke', () => {
         .first();
       await expect(outcome).toBeVisible({ timeout: 30_000 });
     });
+    // Network round trip + UI settle — same magnitude as a login flow.
+    expectWithinBudget(timings, 'upload_file', BUDGET_MS.uiLogin);
   });
 });