refactor: update server URL to handle ipv6

[brenoepics]

Issue for this PR

Closes #18059

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

This PR fixes the ipv6 handling that got broken somewhere during the past 2 weeks, I noticed it after trying to update my production server that uses ipv6, the PR also introduces a new test case to ensure that "127.0.0.1", "0.0.0.0", "localhost", "::", "::1", "[::]", "[::1]" are working for future versions so we don't have this regression again.

Please provide a description of the issue, the changes you made to fix it, and why they work. It is expected that you understand why your changes work and if you do not understand why at least say as much so a maintainer knows how much to value the PR.

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The issue is quite simple: when you are deploying opencode as a coding agent at a cloud network that uses ipv6 (specially for private network traffic), we used to use :: since 0.0.0.0 is ipv4 only, after some change during the past 2 weeks, we started to have a crash on startup: "http://:::4096" cannot be parsed as a URL, yet, 2 weeks ago we had opencode server listening on http://:::4096, I have changed the way we parse the --hostname to ensure we catch ipv6 links and correctly listen fixing it.

How did you verify your code works?

I have run bun dev serve --hostname ::, bun test and I am also using this small patch on my private network while we wait for a next release.

Screenshots / recordings

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Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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