feat: platform browser multi-tab, navigation allowlist, close cleanup, egress filter, allowlist worker wiring

- Multi-tab: browser_new_page / browser_list_pages /
  browser_switch_page / browser_close_page in playwright_mcp.py;
  each new page gets a fresh Playwright context, so cookies and
  storage are isolated between pages. Single-page tools act on
  the current page; switching to a missing index is an error,
  not a crash; closing the last page is an error (use
  browser_close).
- Navigation allowlist: BROWSER_ALLOWED_HOSTS (comma list,
  leading-dot suffix match, case/port-insensitive) checked in
  _check_allowed_url before launching Chromium; unset (or empty)
  means no check, the old behaviour. file:// always allowed;
  localhost/127.0.0.1 have no special treatment.
- Close cleanup: browser_close closes all pages and best-effort
  removes cwd browser-live.png / browser-live.json; custom
  screenshot files are untouched. list_pages needs no launch.
- Egress filter: 10 programming-source Tinyproxy BASIC rules
  (python.org, nodejs.org, go.dev, pkg.go.dev, rust-lang.org,
  developer.mozilla.org, crates.io, stackoverflow.com,
  cve.mitre.org, nvd.nist.gov); already-present github.com /
  pypi.org / npmjs.org not duplicated; searx.diante.me stays
  exact-only, no diante.me wildcard.
- Allowlist worker wiring: _docker_task_context now passes a
  set, non-empty BROWSER_ALLOWED_HOSTS from the worker env into
  [mcp_servers.playwright.env] in the tenant config, so the MCP
  process actually sees it (container -e alone does not reach
  MCP subprocesses, 2026-10-30). Unset/empty writes nothing and
  never overwrites; the value never goes into logs; it is not
  added to the websearch env block or the container env.
  ensure_playwright_mcp_env now returns False without rewriting
  when the result would be identical (canonical join: one blank
  line before the block), so a second prep leaves an unchanged
  tenant config alone; other sections untouched.
- Skill + docs: browser-automation SKILL.md multi-tab/allowlist
  section; docs/platform-browser.md comparison doc (new file).
- Tests (mock/fake only, no network, no real Chromium, no real
  credentials): cloud.tests.test_playwright +
  cloud.tests.test_websearch_worker, 48 tests OK, including 6
  new wiring tests (switch off passes no variable, switch on
  reaches MCP env verbatim, empty never written, old-tenant
  merge idempotent + no-rewrite, ensure no-op when identical,
  allowlist enforces only after wiring).
- NOT done (see PR body): no persistent profile, no credential
  vault, no approval card, no CAPTCHA bypass, in-page link
  navigation does not pass the allowlist, no real-Chromium live
  verification, host tinyproxy filter not reloaded.

deploy/egress/tinyproxy-filter

@@ -45,3 +45,23 @@
 ^\(.*\.\)*weather\.com\.cn$
 ^\(.*\.\)*meteoblue\.com$
 ^\(.*\.\)*accuweather\.com$
+# Platform browser programming sources (2026-11-01, feat-platform-browser).
+# Only programming sources: official docs, GitHub, package registries,
+# Stack Overflow, CVE/NVD. Deliberately NOT included: shopping, social,
+# mail, general news, video sites. Same BASIC form as above.
+# Already present above, not duplicated here: github.com, pypi.org,
+# npmjs.org (plus pythonhosted.org for pip). Notes on coverage:
+# docs.python.org is covered by the python.org line (subdomain rule);
+# docs.rust-lang.org by rust-lang.org; nodejs.org docs live on
+# nodejs.org itself. developer.mozilla.org is scoped to that host
+# only, NOT a mozilla.org wildcard, so no other Mozilla host opens.
+^\(.*\.\)*python\.org$
+^\(.*\.\)*nodejs\.org$
+^\(.*\.\)*go\.dev$
+^\(.*\.\)*pkg\.go\.dev$
+^\(.*\.\)*rust-lang\.org$
+^\(.*\.\)*developer\.mozilla\.org$
+^\(.*\.\)*crates\.io$
+^\(.*\.\)*stackoverflow\.com$
+^\(.*\.\)*cve\.mitre\.org$
+^\(.*\.\)*nvd\.nist\.gov$