fix(web): add web app manifest so installed app keeps its scope

[Albro3459]

What Changed

• Adds apps/web/public/manifest.webmanifest declaring scope and start_url at the origin root, with display: standalone.
• Adds <link rel="manifest" href="/manifest.webmanifest" /> to apps/web/index.html.

Two files, one line of HTML. No new dependencies, no service worker, no new binary assets, no runtime logic, no CSS changes.

Why

Fixes #4305.

apps/web currently ships no web app manifest, so the scope member is never declared. With no scope, iOS infers the navigation scope of an installed Home Screen app from whichever URL was saved.

The app redirects the origin root to the last-opened thread, so the URL captured by "Add to Home Screen" is usually /<environmentId>/<threadId>. Scope collapses to that single thread path, and every subsequent navigation is treated as out of scope and handed off to an in-app browser view, ending the standalone session.

Declaring scope: "/" makes every route on the origin part of the app.

Why the icons reuse existing filenames

scripts/lib/brand-assets.ts swaps web icons by target filename per release channel (nightly-web-apple-touch-180.png and t3-black-web-apple-touch-180.png both land as apple-touch-icon.png).

The manifest therefore references the existing apple-touch-icon.png and favicon-32x32.png rather than adding a new icon asset, so publish-time brand overrides keep applying and nightly builds do not ship the production mark.

Testing

Verified against a real t3 serve build (0.0.29-nightly.20260722.878) served over HTTPS, on iOS 26.5 / Safari.

Server side:

$ curl -s -o /dev/null -w '%{http_code} %{content_type}\n' \
    http://127.0.0.1:3773/manifest.webmanifest
200 application/manifest+json

Mime.getType() in apps/server/src/http.ts resolves .webmanifest correctly, so no MIME handling changes are needed.

Device: added to the Home Screen from a deep-linked thread URL (/<environmentId>/<threadId>), the case that previously broke. Before the change, navigating to another thread left standalone mode and opened an in-app browser view. After the change, navigation stays inside the installed app across threads and Settings.

Deliberately out of scope

• No Android/Chrome installability. The largest existing icon is 180x180 and Chrome wants 192 and 512, but adding icon assets is a separate change.
• No apple-mobile-web-app-* meta tags. Safari 17+ honors display: standalone from the manifest directly.
• No safe-area or app-shell CSS, no push notifications.

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Note

Low Risk
Static manifest plus one HTML link; no auth, data, or runtime logic changes.

Overview
Fixes installed iOS Home Screen behavior when the save URL is a deep-linked thread: without a declared scope, Safari narrows the app to that path and later navigation opens in an in-app browser.

This PR adds manifest.webmanifest with id, start_url, and scope set to /, display: standalone, dark theme colors, and icons pointing at existing favicon-32x32.png and apple-touch-icon.png (so release-channel icon swaps keep working). index.html gains <link rel="manifest" href="/manifest.webmanifest" />.

^{Reviewed by Cursor Bugbot for commit 5449f71. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Add web app manifest to preserve scope when app is installed

Adds manifest.webmanifest and links it in index.html. The manifest sets id, start_url, and scope to /, uses standalone display mode, and declares PNG icons at 32×32 and 180×180 with dark theme colors.

^{Macroscope summarized 5449f71.}

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[macroscopeapp]

Approvability

Verdict: Approved

Adds a static web app manifest file for PWA support. This is a simple configuration-only change with no runtime code modifications - just a JSON file specifying display properties and existing icon references.

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Dismissing prior approval to re-evaluate 1d66bcb