feat(app): embed web ui in binary

[BlankParticle]

What does this PR do?

While building opencode binary, also build the web ui and bundle it with the binary to keep the web ui in sync
also very useful in air gapped systems
extra flag to disable and use hosted version if needed

How did you verify your code works?

Tested web/serve with opencode and checked headers

fixes#8549
fixes#6352
fixes#12445
fixes#12083

and countless related issues

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

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

No duplicate PRs found

[AyRickk]

Any news on this PR ? I'm interested in this feature

[BlankParticle]

Any news on this PR ? I'm interested in this feature

I will ping maintainers on this, they said they were interested in doing this themselves

[Chetic]

Since I'm also very interested in this PR I've tested these changes in a fully air-gapped Docker container (--network none). The container builds the binary from the PR branch, starts opencode serve, and runs Playwright tests against it with a real Chromium browser.

Against v1.2.15 (before this PR), two tests fail:

Test	Why it fails
Web GUI index page loads	Page title is empty — proxy to app.opencode.ai can't connect
SPA routing serves index.html for deep paths	Same proxy issue — /some/deep/path returns empty page

Against this PR branch, both pass.

• / serves a real page — Chromium navigates to the root URL and the page has the "OpenCode" title, meaning index.html is served from the embedded assets instead of proxying to an unreachable external host.
• Deep paths return the SPA shell — Navigating to /some/deep/path no longer returns an empty page. The server falls back to index.html so client-side routing works, which is the expected behavior for a single-page app.

We also verified that all JS/CSS/font assets referenced by index.html load successfully — no failed local requests in Chromium while the page renders.

[farkas93]

Honestly, this should be the default and the way it is done now with the CDN should get a disclaimer and an explanation for when and how that is useful? It just destroyed quite some trust towards this project realizing that the team went an extra mile to separate the webUI from the server, only to take away control from the user on what webUI code they are running.

[thdxr]

had to make some changes to this PR and had to move it to a new branch so closing this for now

[BlankParticle]

had to make some changes to this PR and had to move it to a new branch so closing this for now

no worries, nice to see this getting shipped at last, I almost gave up on this lol

[farkas93]

could someone link the branch where this feature was moved pls?

[capi]

@farkas93 As far as I understood #19217 (comment), this is now part of 1.3.3