feat: add orbit-blur transparent background + Gaussian blur plugin

[c0sc0s]

Summary

Adds @c0sc0s/orbit-blur, a renderer-only Orbit plugin that injects transparent Codex chrome backgrounds and Gaussian backdrop-filter blur (frosted-glass) when enabled.

• New package packages/orbit-blur with orbit-plugin.json, esbuild IIFE bundle (runtime/dist/injected.js), and SDK type-only activation
• Defaults: blurPx: 18, tintOpacity: 0.42 (overridable via plugin config)
• Landmark/role CSS only — no private Codex DOM selectors, no service process
• Wired into monorepo build / check / CI bundle freshness check

Enable / test locally

npm run build -w @c0sc0s/orbit-blur
node packages/orbit/dist/cli.js plugin add ./packages/orbit-blur
node packages/orbit/dist/cli.js plugin enable orbit-blur
# with Codex already CDP-debuggable:
node packages/orbit/dist/cli.js apply   # or npm run dev:apply after registering

Verification

• npm run verify — passed
• git diff --check — clean
• manage.mjs install / apply — skipped (Codex/CDP unavailable in this environment)

Notes / open questions

• True OS-level window transparency still depends on Electron host settings; this plugin only styles the renderer. Backdrop blur still frosts in-app content under chrome.
• Surfaces targeted: html/body transparency, CSS background tokens when present, landmark chrome (aside/nav/header/ARIA roles), #root/#app, dialogs. May need tuning against live Codex DOM.