feat(figma): live-preview onboarding, eager sync, per-file state & UX polish

[piaskowyk]

What & why

A batch of Figma-plugin and PulsarApp UX improvements around the live-preview / onboarding flow.

Figma plugin

Sync goes live automatically

• Configuring the live preview (a valid Figma file key) — or copying the share link — now starts syncing with the backend instead of sitting at "Not shared yet".
• On first open, the plugin eagerly provisions the backend project if this file has none yet, so the share link and pairing QR exist from the start. It's create-only (never overwrites an existing project) and runs through the same publish lock (no duplicate rows).

Per-file state (fixes "new project" bugs)

• onboardingSeen and the phone-pairing token were stored per-user globally, so a new project never re-showed the onboarding tour and inherited a stale token that appeared as a "paired but offline" phone — which also wrongly collapsed the first configurator step and lit an amber warning dot.
• Both are now namespaced per-file (per-user-per-file), so a new project starts clean: the tour shows on first visit, and step 1 opens with no phantom pairing.

Onboarding / explanation videos

• Wired the clips into the tour and the two Live-preview steps. Hosted remotely (off-bundle — inlining was ~49 MB; now ~0.5 MB) via GitHub attachment URLs, with the S3 host allowlisted in manifest.json.
• Each clip has native controls, a spinner + placeholder while buffering, and an "Open full size video" link (opens via open-external).
• Clips are preloaded (persistent elements) so paging between steps / expanding step 2 doesn't re-buffer.
• Added a new tour step: "Preview a preset on your device."

Legible step hand-off

• When step 1 is completed, the accordion now runs a staged sequence — green pulse → collapse step 1 → fade in step 2 → open step 2 — instead of snapping instantly, so an accepted file key registers. Includes a real height animation (native <details> can't animate) and honors prefers-reduced-motion.

Help tab

• Example-file link now points at the real Figma file.

PulsarApp

• WebView loader fix: the Figma-preview loader now clears once content is ready and is non-blocking, so if the preview falls back to a Figma login page the button isn't trapped behind the spinner.
• Now-playing banner: the "<preset> is playing!" banner now also shows on the Figma screen (extracted to a shared NowPlayingToast), not just Home.

Reviewer notes

• GitHub-hosted videos are interim. The asset is tied to the upload comment and the S3 URL is short-signed; before a public release these should move to a durable host (e.g. pulsar-server.swmansion.com, already allowlisted) and the two GitHub/S3 manifest entries dropped.
• The eager first-open provisioning means opening the plugin on any file now creates a backend row (deliberate reversal of the old "don't create until shared" policy).
• Per-file token migration: existing users will re-pair once per file and see the tour again once per file after this lands.
• Verified via tsc --noEmit + vite build (plugin) and tsc --noEmit (PulsarApp). The plugin/app surfaces need a load in Figma / a device to exercise end-to-end.