test: activate the full e2e (browser-driving) suite + add fetch --force

The 138 @pytest.mark.e2e tests were doubly inactive: deselected by addopts AND
skipped without a cached binary — and 3 of the 6 per-file firefox_binary
fixtures silently ignored INVPW_BINARY_PATH, so they'd test whatever was cached
even when you pointed the suite elsewhere (a false-confidence trap).

- Centralize firefox_binary into conftest.py (env INVPW_BINARY_PATH → cache →
  skip); delete the 6 duplicates. Unify test_webrtc_realness onto the same env.
- scripts/run_e2e.py: one command that runs ALL e2e against a chosen binary,
  with reruns so an under-load interaction flake (dblclick/hover pass 3/3 in
  isolation) self-heals while a real break fails every attempt. The webrtc e2e
  fake a TCP-only SOCKS locally, so the suite is offline. This is the MANDATORY
  pre-release browser gate (local — hosted runners are too interaction-flaky).
- Running the suite against firefox-9 surfaced a real gap: `invisible_playwright
  fetch --force` was unrecognized (the subparser took no args) though the e2e
  test + docstring expect it. Implement it: drop the cached version dir, refetch.
- Add pytest-rerunfailures + playwright to the dev extras.

Baseline against firefox-9: 136 passed, 1 skipped (linux_only on win host),
1 was the --force gap now fixed.

scripts/run_e2e.py

@@ -0,0 +1,67 @@
+#!/usr/bin/env python3
+"""Run the FULL e2e suite (every test that opens the browser) against a binary.
+
+The 138 ``@pytest.mark.e2e`` tests are excluded from the default `pytest` run
+(`addopts = -m 'not slow and not e2e'`) because they need a real Firefox binary
+and a display, and they skip themselves when no binary is available. That makes
+them easy to forget — and "we can't afford for something to not work". This is
+the gate that runs them all, deliberately, against a chosen binary.
+
+It is the MANDATORY pre-release e2e gate: run it green against the freshly-built
+release binary BEFORE un-drafting a firefox-N (alongside the fppro + WebRTC
+realness gates). It is NOT in the public CI drive-gate — the hosted runners are
+content-process unstable under a heavy headless interaction sequence (see
+70-known-bugs / 60-ci-release-pipeline); this runs locally on reliable hardware.
+
+Flake-resilience: under full-suite load a couple of interaction tests (dblclick,
+hover/mouseenter) can flake even though they pass 3/3 in isolation, so failures
+are reran up to twice on the known transient signatures. A genuinely broken
+binary fails all attempts. The webrtc e2e fake a TCP-only SOCKS locally (no
+proxy/secrets), so the whole suite is offline.
+
+Usage:
+    python scripts/run_e2e.py <firefox-binary>
+    python scripts/run_e2e.py            # uses $INVPW_BINARY_PATH
+"""
+from __future__ import annotations
+
+import os
+import subprocess
+import sys
+from pathlib import Path
+
+_RERUN_SIGNATURES = "Timeout|context was destroyed|was detached|not visible|because of a navigation|TargetClosed"
+
+
+def main() -> int:
+    binary = sys.argv[1] if len(sys.argv) > 1 else os.environ.get("INVPW_BINARY_PATH")
+    if not binary:
+        print("usage: run_e2e.py <firefox-binary>  (or set INVPW_BINARY_PATH)", file=sys.stderr)
+        return 2
+    if not Path(binary).exists():
+        print(f"ERROR: binary not found: {binary}", file=sys.stderr)
+        return 2
+
+    env = dict(os.environ)
+    # One setting drives the whole suite: conftest's firefox_binary fixture and
+    # the webrtc e2e both resolve from these.
+    env["INVPW_BINARY_PATH"] = binary
+    env["STEALTHFOX_E2E_BINARY"] = binary
+
+    repo = Path(__file__).resolve().parent.parent
+    cmd = [
+        sys.executable, "-m", "pytest",
+        "-m", "e2e",
+        "-o", "addopts=",            # override the default 'not e2e' deselection
+        "--reruns", "2", "--reruns-delay", "1",
+        "--only-rerun", _RERUN_SIGNATURES,
+        "-p", "no:cacheprovider",
+        "-q", "--tb=short",
+    ] + sys.argv[2:]
+    print(f"[run_e2e] binary={binary}")
+    print(f"[run_e2e] {' '.join(cmd)}")
+    return subprocess.run(cmd, cwd=repo, env=env).returncode
+
+
+if __name__ == "__main__":
+    sys.exit(main())