fix: backport upstream playground, vanilla, Angular and FAQ changes (batch 2)

[Project516]

Backports from upstream #977 and #980, adapted to this fork.

• Playground: arguments that are invalid JSON or not a list of strings no longer crash the page. A shared parseArgs returns [] for them, used both for the preview and for Run (the preview called data.join on any parsed value, and Run called exec(JSON.parse(args)) directly).
• Vanilla example: download-assets.js moves into apps/vanilla-app so the example no longer reaches outside its directory. Unlike upstream it keeps core-mt, since the mt pages still use it. release.yml now checks the script at its new path. The scripts use pnpm in the README.
• Angular example: Angular does not bundle the library's worker, so worker.js 404ed. angular.json copies @project516/ffmpeg-wasm/dist/esm/*.js to /ffmpeg and load() gets classWorkerURL. The example now uses the single-thread core (the dev server sends no COOP/COEP headers) and drops the no-op workerURL.
• FAQ: new or rewritten entries on speed, RTSP, input size and WORKERFS, log types, raw frames, and WebM alpha, written for this fork's memory limits (st core starts at 48 MB, mt at 1 GB, both capped at 2 GB).

Not run locally (Raspberry Pi, no Docker or example installs): the Angular build, the vanilla download script, the website build or type check, and upstream's e2e additions (tests/ is out of scope for this PR). The -sws_flags accurate_rnd+bitexact advice and the WORKERFS snippet are carried over from upstream behavior and not tested against this fork's cores.

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📥 Commits

Reviewing files that changed from the base of the PR and between 36bf577 and 330eb95.

📒 Files selected for processing (9)

• .github/workflows/release.yml
• apps/angular-app/angular.json
• apps/angular-app/src/app/app.component.ts
• apps/vanilla-app/README.md
• apps/vanilla-app/download-assets.js
• apps/vanilla-app/package.json
• apps/website/docs/faq.md
• apps/website/src/components/Playground/Workspace/Editor.tsx
• apps/website/src/components/Playground/Workspace/index.tsx

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[project516-review-bot]

This PR backports playground safety fixes, vanilla app reorganization, Angular worker handling, and FAQ updates from upstream. The playground now shares a parseArgs helper that safely returns [] for invalid JSON or non-string arrays, preventing crashes in both preview and Run. The vanilla example moves download-assets.js into its own directory and switches to pnpm commands. The Angular example switches to the single-thread core and uses classWorkerURL with a copied worker file since the dev server lacks COOP/COEP headers. The FAQ adds entries on performance, RTSP, input limits, WORKERFS, log types, raw frame differences, and WebM alpha.

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_{review-bot, model nvidia/nemotron-3-ultra-550b-a55b:free, verdict approve}