Add multi-framework support to create-refrakt

Extend create-refrakt to scaffold projects for Astro, Nuxt, Next.js, and Eleventy in addition to the existing SvelteKit and HTML targets.

Context

create-refrakt currently supports two targets: --target sveltekit (default) and --target html. With SPEC-030 delivering framework adapters, the scaffolding tool needs to generate correct project templates for each supported framework — appropriate config files, dependencies, routing boilerplate, and starter content.

Acceptance Criteria

--target astro scaffolds an Astro project with astro.config.mjs, @refrakt-md/astro integration, BaseLayout.astro usage, getStaticPaths() content loading, behavior init script, and starter content
--target nuxt scaffolds a Nuxt project with nuxt.config.ts, @refrakt-md/nuxt module registration, catch-all route pages/[...slug].vue with RefraktContent, useRefraktMeta composable usage, and starter content
--target next scaffolds a Next.js App Router project with app/layout.tsx (CSS import), app/[...slug]/page.tsx (RSC content loading + RefraktContent + BehaviorInit), generateStaticParams, generateMetadata helper usage, and starter content
--target eleventy scaffolds an Eleventy 3.0 project with .eleventy.js plugin config, _data/refrakt.js global data file, base.njk template, pagination config, CSS passthrough copy, behavior script inclusion, and starter content
Each target generates correct package.json with framework-appropriate dependencies (peer deps, dev deps) using the same ~version coupling strategy as existing targets
Each target generates correct refrakt.config.json with appropriate target field
Starter content (_layout.md, index.md, docs/getting-started.md) is shared across all targets — only the surrounding framework boilerplate differs
Interactive mode when --target is not provided: prompts for project name (if not given as positional arg) and target selection from a list (SvelteKit, Astro, Nuxt, Next.js, Eleventy, HTML)
CLI help text and post-scaffold "next steps" messages are framework-appropriate
site/content/docs/adapters/ overview page updated to list all available targets
Existing tests updated; new tests cover each target's generated file structure, dependency versions, and config correctness

Approach

Each new target needs a template directory (template-astro/, template-nuxt/, template-next/, template-eleventy/) containing framework boilerplate files. The scaffold.ts logic already handles target selection via the --target flag — extend the switch to dispatch to new template directories.

Starter content files (content/) are identical across targets and can be symlinked or copied from a shared location to avoid duplication.

Dependency versions follow the existing pattern: @refrakt-md/* packages use ~${getRefraktVersion()}, framework deps use pinned semver ranges (e.g., astro@^5.0.0, nuxt@^3.0.0, next@^14.0.0 || ^15.0.0, @11ty/eleventy@^3.0.0).

Interactive mode is the default when --target is omitted. Running npx create-refrakt (or npx create-refrakt my-site without --target) presents a list of framework targets to choose from. The --target flag remains available for CI and scripted usage. Use a lightweight prompting library (e.g., @inquirer/prompts or @clack/prompts) — keep the dependency small.

Dependencies

WORK-089 (Astro adapter exists)
WORK-090 (Nuxt adapter exists)
WORK-091 (Next.js adapter exists)
WORK-092 (Eleventy adapter exists)

Note: Templates can be written before adapters ship, but the scaffolded projects won't work until the corresponding adapter package is published. Consider gating targets behind adapter availability or scaffolding with a "coming soon" note.

References

SPEC-030 (Framework Adapter System)
WORK-052 (project-type defaults — complementary, covers package pre-selection)
packages/create-refrakt/src/scaffold.ts — existing scaffolding logic
packages/create-refrakt/template/ — SvelteKit template (reference for new templates)
site/content/docs/adapters/ — existing adapter documentation