docs(known-issues): record pre-existing e2e flakes + firefox CDN spec

Full test battery run (unit, dm, smoke, e2e, visual). Document the non-regression
e2e failures found:
- login-flows:149 and video-upload-publish-lifecycle:49/:79 flake under full
  parallel load, pass in isolation (worker contention).
- webseed-playback:31 fails on Firefox headless only (CDN mode); pre-existing
  (reproduced on 1b11cb1b), Chromium + WebTorrent-fallback variants pass.

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

KNOWN_ISSUES.md

@@ -21,3 +21,15 @@
 - **Status:** Addressed
 - **Description:** `tests/nostr-send-direct-message.test.mjs` must pass `Uint8Array` secret keys to `getPublicKey/finalizeEvent` for current `nostr-tools`.
 - **Impact:** Passing hex strings causes failures like `expected Uint8Array, got type=string`.
+
+## Run Notes (2026-06-20)
+
+### Additional E2E specs flake under full parallel load (pass in isolation)
+- **Status:** Active
+- **Description:** Under the full `test:e2e` run (378 tests, 4 workers) these intermittently fail on `not.toBeVisible`/feed-appearance timeouts, but pass deterministically when re-run in isolation (`--workers=1`): `login-flows.spec.ts:149` (upload/profile buttons hide after logout), `video-upload-publish-lifecycle.spec.ts:49` and `:79` (URL-first publish appears / owner delete). Same root cause as the Firefox feed-hydration flakes above — worker resource contention, not an app regression (verified: pass in isolation on the current branch).
+- **Impact:** Full-suite e2e is flaky; isolated reruns are green.
+
+### `webseed-playback.spec.ts:31` fails on Firefox headless (CDN mode)
+- **Status:** Active (pre-existing — reproduced on pre-refactor commit `1b11cb1b`)
+- **Description:** "plays directly from HTML link (CDN mode)" fails on `--project=e2e-firefox` with `#modalVideo` `src` empty instead of the test's archive.org URL. The Chromium variant and the WebTorrent-fallback variant (`:63`) both pass. Firefox-headless-specific (external URL reachability/codec), not an app regression.
+- **Impact:** One Firefox-only e2e failure; CDN playback works on Chromium and in manual testing.