fix(🐛): don't crash the web view when no WebGL surface can be created

[wildan-m]

Description

On web, WebGLRenderer in SkiaPictureView.web.tsx throws when the browser cannot provide a WebGL surface — hardware acceleration disabled, a blocklisted GPU, a GPU process restart, or the per-page live-context limit being exhausted. Both throw sites escape as uncatchable errors:

• the constructor throws inside the useLayoutEffect that builds the renderer, and
• onResize throws inside the ResizeObserver callback,

so no try/catch or React error boundary in the embedding app can reach them, and an environmental limitation becomes an app crash. We (Expensify) see this at scale in production Sentry as failed to create webgl context: err 0 / Could not create surface from chart views on /home and /search (Sentry issue APP-7MV: hundreds of users, thousands of events), currently worked around with a patch-package patch.

Change

Degrade instead of throwing, mirroring how StaticWebGLRenderer already treats a failed surface as recoverable rather than fatal:

• When no WebGL/graphics context or on-screen surface can be created, leave the renderer inert — draw(), makeImageSnapshot() and onResize already no-op on a null surface/grContext, and dispose() already handles the null fields.
• Dispatch a bubbling skia-surface-unavailable CustomEvent on the canvas so embedders can detect the condition and show a fallback UI (deferred one frame so listeners attached in an effect of the same commit are registered first). Without a listener the event is a no-op, so existing consumers see no behavioral change other than not crashing.

Notes

• No API change; capable clients are unaffected.
• The event lets an app render its own "chart unavailable" state — a capability check before mounting cannot cover this, because the surface is created after the CanvasKit WASM module loads and WebGL availability can change in between.

Test plan

• Simulated an incapable client in Chrome by making HTMLCanvasElement.prototype.getContext return null for "webgl2": previously the uncaught throw surfaced and the canvas stayed blank; with this change the view mounts inert, the event fires on the canvas, and a listener can swap in fallback UI. Restoring WebGL and remounting renders normally.
• Verified prettier --check (2.8.7) passes on the touched file.

[wildan-m]

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