fix: browser tests failing because containers can't find Redis

[asmit27rai]

Fixes #787

What was happening

All 42 browser tests (chromium, firefox, webkit) were failing because
the containers couldn't find transport-redis by name.

What I changed

1. Told Docker which DNS to use (run-single-test.sh)

• Added dns: 127.0.0.11 to the docker-compose template
• This is Docker's built-in DNS server — makes sure containers
  always know how to find each other by name

2. Added retry logic (.aegir.js in v1.x, v2.x, v3.x)

• Instead of trying to connect to Redis once and dying, now it
  tries 10 times with a short wait between each attempt
• If it connects on the first try (normal case), nothing changes

3. Fixed a potential broken DNS config file (BrowserDockerfile in v1.x, v2.x, v3.x)

• Playwright install can sometimes break /etc/resolv.conf
• Added a check that fixes it if it's broken, does nothing if it's fine

Files changed

• transport/lib/run-single-test.sh — dns config in compose template
• transport/images/js/v1.x/.aegir.js — retry logic
• transport/images/js/v2.x/.aegir.js — retry logic
• transport/images/js/v3.x/.aegir.js — retry logic
• transport/images/js/v1.x/BrowserDockerfile — resolv.conf fix
• transport/images/js/v2.x/BrowserDockerfile — resolv.conf fix
• transport/images/js/v3.x/BrowserDockerfile — resolv.conf fix

[dhuseby]

I have a PR landing that I think also fixes this problem.