Install the capture snippet without an agent for common frameworks

[nrodd]

Summary

Step 1 (installing the capture snippet) no longer needs a coding agent for the frameworks we recognize. The wizard detects the framework, previews the exact lines it will add, and writes them once the user confirms. Anything it can't place with certainty goes to the agent-driven install, which is unchanged.

Supported

Framework	Edit
Next.js App Router	<Script strategy="beforeInteractive"> in the root layout's <head> (or first in <body>), adds the next/script import if missing
Next.js Pages Router	inside <Head> in _document, or creates _document
Remix / React Router v7	inside <head> in app/root
Nuxt 3+	adds app.head.script to nuxt.config
Gatsby	creates gatsby-ssr with onRenderBody
Astro	the single layout with a <head>, as <script is:inline>
SvelteKit, Angular, Vite, CRA, Vue CLI, plain HTML	before </head> in the entry HTML

JS/TS edits use @babel/parser to find insertion points and splice text, so the rest of the file's formatting is untouched, and the edited file must parse again before it's written. A write is refused if the file changed after the preview.

Falls back to the agent when

Monorepo roots, React Native, unsupported frameworks (TanStack Start, SolidStart, Qwik, Redwood, Ember), Nuxt 2, any detected Content-Security-Policy (including helmet / nuxt-security), mixed App/Pages Router, custom appDirectory or Vite root, multi-page Vite apps, an existing gatsby-ssr or Nuxt app block, zero or several <head>s, unparseable files, a declined edit, or a failed write.

Flow changes (run.ts)

• After a static install (or an already-installed snippet), the step-1 prompt review and handoff are skipped on the terminal, app, and manual paths; the agent is still picked for session review and step 2.
• The wizard reports precheck/explore/plan/install itself, so the funnel shape is unchanged.
• --print-prompt previews the edit without writing.

Other

• @babel/parser is now a runtime dependency (was already in the lockfile transitively).
• README and a changeset are updated.

Test plan

• npm test: new suite with throwaway projects for every framework and fallback case (88 tests passing)
• npm run typecheck, npm run build
• Mock end-to-end run against a scratch Vite project
• Try it against a fresh create-next-app (App and Pages Router) and a Nuxt starter