docs: polish root README and add per-package READMEs

[ignsm]

Root README

Fixes three kinds of issues against the writing rules in CLAUDE.md:

• Em dashes removed from tagline (Define a form once — fields, validation, ... — in a single file → parens).
• Marketing-speak trimmed: its own compact, There is also a Figma plugin, Useful for rapid prototyping and design handoff all cut or rephrased.
• Broken playground links fixed. Two links pointed at https://formhaus.dev/playground and /playground (relative), both 404 on the deployed site. Now both point at https://formhaus.dev/playground.html which is the real deployed URL.

The Figma plugin mention was also clarified: Available via manifest.json for now was too cryptic for people who haven't installed a local Figma plugin before. Now says explicitly: "Not on Figma Community yet, install as a local plugin via packages/figma/manifest.json".

Per-package READMEs

All four published packages had empty npm pages (no readme field in the published tarball). Verified by checking registry.npmjs.org/@formhaus/core/0.3.1 which has no readme or readmeFilename. npm auto-includes README.md from the package directory regardless of files whitelist, so these will appear on npm on the next publish.

Each package gets a focused README:

• packages/core/README.md — zero-dep engine usage example with FormEngine, setValue, validate, getSubmitValues. Lists what the engine covers (visibility, multi-step, async validation, definition validation).
• packages/react/README.md — React adapter, <FormRenderer definition={...} /> example, components prop for custom UI kit.
• packages/vue/README.md — same for Vue 3 with <script setup> and :definition prop.
• packages/figma/README.md — different shape: it's a Figma plugin, not an npm lib usage. Walks through local plugin install (clone, build, Figma Plugins → Development → Import plugin from manifest), usage, and component map config.

All four link back to https://formhaus.dev, https://formhaus.dev/playground.html, and the GitHub repo.

Effect on published packages

None until the next publish. This PR is docs-only, no code changes, no package.json changes. The README files will ship automatically with @formhaus/core@0.3.2 / @formhaus/react@0.3.2 / etc. whenever the next release goes out.

Test plan

• pnpm build && pnpm test still green (unchanged, but sanity)
• After merge + next publish: npm pages for all four packages show a README
• Root README renders correctly on github.com/ignsm/formhaus (em dashes gone, playground links work)

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Project	Deployment	Actions	Updated (UTC)
formhaus	Ready	Preview, Comment	Apr 10, 2026 3:49pm