feat: introduce PurplePrint Studio identity

[PurplePrintAI]

Summary

• Rebrand the independent OpenScreen fork as PurplePrint Studio across the editor, capture entry surfaces, app menus, icons, installer name and localized copy.
• Apply GraphOS-family neutral surfaces and restrained violet accents while preserving functional recording/status colors and the existing light-mode preference.
• Keep the technical app ID, user-data profile, .openscreen project format, CLI command and fork update origin stable. Document upstream provenance and keep Design Coach/MCP integration out of this frontend identity change.
• Make fresh Windows worktree builds stage the pinned FFmpeg SDK reliably, without writing through SDK links or deleting an unexpected extraction path.

Release impact

• This is an unreleased branding change, based on fork/main. No GitHub Release has been published. The owner approved a local Windows installation for validation.
• The Windows NSIS candidate is version 1.10.0-subscription.8 and is unsigned. Public publication requires separate approval.
• Physical HUD mouse reachability, installed-app updater behavior from the renamed child directory, real Mac record/edit/export and Developer ID signing/notarization remain open release gates. Design Coach/MCP integration belongs to its separate workstream.

Validation

• npm ci with Node 22.22.1 / npm 10.9.4.
• npm test: 189 files, 2,252 passed, 4 skipped.
• App and test TypeScript checks, Vite build, docs check and i18n check passed; Biome passed with 13 pre-existing warnings.
• npm run build:win:fork completed from this worktree after checksum-verified FFmpeg and speech staging.
• Packaged Windows app launched with an isolated user-data directory; PurplePrint Studio title and fork update origin verified.
• Before the live upgrade, the installed .7 fork created a synthetic-media project in an isolated profile. The .8 package retained the clip, light theme and preferences and exported a decodable MP4.
• The owner-approved .8 installer reused the per-user uninstall registration, removed the old executable, created a product-named child directory under the prior custom install root, and replaced the Start-menu shortcut. A verified local backup preceded installation. Three live project files and the AI configuration retained their hashes; private project contents were not opened/exported for this check.
• The installed .8 executable loaded copies of all three real project documents (three assets, three clips, three accessible media paths) and opened the editor in a separate test profile; no titles or footage were emitted.
• Packaged Windows WGC recorded a generated QA window with microphone, system audio and camera off; the saved project reopened and exported a decodable MP4. This used automated renderer control, so it does not prove physical click-through HUD behavior.
• macOS validation run 36320426373 built Apple Silicon and Intel DMGs with the corrected Studio installation guide. Both passed architecture, native payload, bundle ID, ad-hoc signature, CLI boot and mounted-DMG checks. Downloaded DMGs matched their SHA-256 manifests; neither is notarized.

Review focus

• Visual identity and upstream attribution.
• Technical identity, profile continuity and updater behavior after the installed path transition.
• FFmpeg SDK staging behavior on Windows and Linux.