Add portable wrapper scripts and usage guide

[jek-bao-choo]

Issue for this PR

Closes #15789

Type of change

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

What does this PR do?

Adds self-contained portable wrapper scripts that let users run OpenCode without a global install, PATH changes, or files written to their home directory. Everything lives inside a .opencode_portable/ directory
next to the script.

What's included:

• opencode-portable.sh — Bash wrapper for macOS and Linux. Handles architecture detection (ARM64/x64, Rosetta), musl vs glibc, AVX2 baseline fallback, and auto-downloads the correct binary from GitHub Releases.
• opencode-portable.ps1 — PowerShell wrapper for Windows. Same download/version logic adapted for PowerShell 5.1+.
• PORTABLE-GUIDE.md — Usage guide covering prerequisites, how to download the wrapper scripts, quick start per platform, version pinning (env var or .opencode-version file), installing external skill plugins,
  and troubleshooting common issues.

Both scripts isolate all state via XDG environment variables (XDG_CONFIG_HOME, XDG_DATA_HOME, etc.) pointed at the portable directory, and disable auto-update so the wrapper controls versioning.

How did you verify your code works?

• Ran opencode-portable.sh on macOS (Apple Silicon) — confirmed it downloads the correct darwin-arm64 binary, creates the .opencode_portable/ directory structure, and launches OpenCode successfully.
• Tested --portable-update, --portable-version, and --portable-help flags.
• Tested version pinning via OPENCODE_PORTABLE_VERSION env var and .opencode-version file.
• Reviewed PORTABLE-GUIDE.md renders correctly in GitHub Markdown preview.

Screenshots / recordings

Checklist

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

[github-actions]

Hey! Your PR title Add portable wrapper scripts and usage guide doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potentially Related PRs Found:

1. PR feat: add directory override env vars and OPENCODE_APPNAME for portable mode and profile isolation #8963: feat: add env vars for complete portable mode and isolation support

   • feat: add directory override env vars and OPENCODE_APPNAME for portable mode and profile isolation #8963
   • Likely related: This PR adds environment variables for portable mode and isolation, which complements the wrapper scripts in PR Add portable wrapper scripts and usage guide #15786 that use XDG environment variables for complete isolation.

2. PR feat(opencode): added portable static builds #9430: feat(opencode): added portable static builds

   • feat(opencode): added portable static builds #9430
   • Likely related: This PR adds portable static builds, which is foundational to the wrapper script functionality in PR Add portable wrapper scripts and usage guide #15786 that downloads these portable binaries.

These PRs appear to be building blocks or related work in the portable/self-contained installation space, though PR #15786 is the primary implementation of the user-facing wrapper scripts and guide.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[github-actions]

Closing this pull request because it has had no updates for more than 60 days. If you plan to continue working on it, feel free to reopen or open a new PR.