feat: Adding basic PWA support

[jetpham]

Issue for this PR

Closes #19174

Type of change

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

What does this PR do?

This adds basic PWA support for the web app so OpenCode feels more like an installed app and can keep its core shell available offline.
I added the mobile web app metadata in packages/app/index.html, updated the manifest with install settings like start_url, scope, fullscreen display options, and icon purposes, and registered a service worker from packages/app/src/entry.tsx. The new packages/app/public/sw.js caches the app shell and key static assets, uses cached assets when it can, and falls back to the cached root document for navigation requests when the network is unavailable. I also updated packages/app/public/_headers so the manifest and service worker are served with the right content types and service worker headers.
This works because browsers need the manifest, install metadata, and service worker together for installability and offline support. Caching the shell assets gives the app something reliable to load when the network drops, and the added headers make sure those files are recognized and scoped correctly by the browser. One thing I like is that this keeps a single persistent instance of the app open rather than opening multiple instances in the browser.

How did you verify your code works?

I ran the opencode web application and served it locally onto my network, then opened it on my phone and installed the PWA. Screenshots attached.

Screenshots / recordings

Checklist

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

[github-actions]

Hey! Your PR title Jet/pwa support 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:

I found a potential duplicate:

• PR fix(app): add PWA service worker for asset caching #19122: fix(app): add PWA service worker for asset caching

This PR appears to directly address the same feature as PR #19173. Both PRs are implementing PWA (Progressive Web App) support with a service worker for caching assets. PR #19122 specifically mentions "add PWA service worker for asset caching," which overlaps with the core functionality described in the current PR (registering a service worker to cache the app shell and static assets).

[github-actions]

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

[masrurimz]

got similiar PR #19122
hope this can be merge soon

[squat]

I'm eager to test out this patch on my install but there seems to be a merge conflict with index.html that prevents the patch from applying cleanly. Could you rebase?

[squat]

🚀 I added this PR as a patch on my Nix derivation for opencode and can confirm this works!

[jetpham]

I hit Test timeout of 60000ms exceeded. . The windows CI is broken