fix(webgl): cache support probe so it creates a context at most once

[chiefcll]

What

getWebglSupportedVersions (src/utils.ts) creates a real WebGL context (canvas.getContext) to detect support, but it only cached the result when called with the default id list (reference equality against the internal WEBGL_CONTEXT_IDS). Any caller passing its own array — which our app does — bypassed the cache and created a new WebGL context on every call.

This PR:

• Caches per distinct id list (a Map keyed on the joined ids), so a probe context is created at most once per page, regardless of how the caller invokes it.
• Releases the probe context via WEBGL_lose_context, guarded by isContextLost() so we never call loseContext() on a context the browser already evicted.

Why

Reported on Apollo/Sunrise TV boxes (Chrome 38+). The device console showed, all originating at this function:

There are too many active WebGL contexts on this page, the oldest context will be lost.
WebGL: INVALID_OPERATION: loseContext: context already lost
Could not create WebGL Texture            (renderer: WebGlCtxTexture)
Failed to upload texture: ...             (renderer: CoreTextureManager)

Embedded TV SoCs cap the number of live WebGL contexts very low. Re-probing on every call blows that budget; the browser evicts the oldest context — the live render context — and the renderer then fails every createTexture(), spamming Could not create WebGL Texture each requestAnimationFrame. A prior loseContext-only attempt didn't help (and produced the context already lost error) because the eviction happens at context creation time — the cure is to stop creating contexts repeatedly.

Notes for reviewers

• Detection output is unchanged for any given argument. The single-canvas probe logic (and therefore supportsWebGL / supportsWebGL2 / supportsOnlyWebGL2 results) is identical — only the number of contexts created changes (now: one per arg list, ever).
• The companion renderer-side leak (detectPremultiplyAlphaHonored) is fixed separately in solid-tv/renderer: fix(webgl): release throwaway context in premultiply-alpha probe renderer#114
• Follow-up worth considering at the call site: invoke detection once at startup, before the renderer is created, so even the first probe can't evict a live render context.

Tests

New tests/webgl-support.test.ts (4 tests) asserts the behavioral guarantees:

• probe context is created at most once across repeated calls
• loseContext is skipped when the context is already lost
• probe context is released (lose-context extension requested)
• no throw when WebGL is unavailable

npx vitest run → full suite 134/134 pass; tsc --noEmit clean; prettier + eslint clean.

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