Add Webxdc packaging via make build-xdc

[omidz4t]

Summary

Adds a way to package squig as a Webxdc mini-app for Delta Chat, without changing the normal production build used for squig.sh.

• make build-xdc runs a static export (WEBXDC=1) and zips out/ into dist/squig.xdc
• When WEBXDC=1, Next uses output: "export" and unoptimized images; plain pnpm build is unchanged
• Ships public/manifest.toml + icon.png for the messenger; public/webxdc.js is a local-dev shim and is excluded from the zip (the host injects its own)
• Marks the social image routes force-static so static export can succeed

What is Webxdc?

Webxdc is a format for small web apps that run inside a chat message (most commonly in Delta Chat). A .xdc file is just a zip of static assets — HTML, JS, CSS, images — plus a manifest.toml (and usually an icon) at the root of the archive.

When someone sends the file into a chat and taps Start, the messenger opens it in an embedded webview. There is no app store and no separate install step: the app travels with the message. State can stay local in the webview (e.g. localStorage), and apps that need multi-user sync can use the host’s window.webxdc API (sendUpdate / setUpdateListener, etc.). That API is provided by the messenger at runtime — projects often keep a stub webxdc.js for browser development, but it must not be shipped inside the .xdc.

This PR only packages squig as a self-contained offline app. It does not add multiplayer sync over webxdc updates; documents still live in the browser’s storage, same idea as on the web.

Docs: webxdc.org · spec

Later plan: realtime collaboration

Out of scope for this PR. Once the static package is solid, a follow-up can add multi-user editing the same way as omidz4t/excalidraw-webxdc:

• Document sync over Delta Chat’s sendUpdate / setUpdateListener (likely Yjs + something like y-webxdc, as in that fork)
• Live strokes / cursors on the messenger’s P2P realtime channel (Delta Chat 1.48+), so peers see each other draw without waiting on full updates
• Multi-peer local testing with @webxdc/webxdc-dev (same pattern as make run-sim there)

Until then, each open instance keeps its own local file drawer; sharing a canvas across a chat is intentionally not wired yet.

Test plan

• pnpm build still succeeds (server / squig.sh path)
• make build-xdc produces dist/squig.xdc containing index.html, manifest.toml, and icon.png
• Confirm webxdc.js is not inside the .xdc
• Open dist/squig.xdc in Delta Chat (or webxdc-dev) and check the canvas loads and basic drawing works offline

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[omidz4t]

Hey — if you’re interested, I’d be happy to help make squig collaborative in Delta Chat later (same general approach as excalidraw-webxdc: document sync + live cursors over the messenger).

I think this project has a lot of potential when people can use it inside Delta Chat — wireframing together in a chat feels like a natural fit for how squig already works (local files, sketchy fidelity, no accounts).

Also, if you get a chance, it would be nice if you could try the Excalidraw webxdc port for a feel of how collab works in that setup: https://github.com/omidz4t/excalidraw-webxdc

Happy to iterate on feedback either way. Thanks for squig!