[#68 / 2] Form basics — Label, Input, Field, InputGroup

[fedorovvvv]

Group 2 of 8 — sub-issue of #68 (PRD-018 / RFC-016).

Scope

Form-input atoms — pure CSS, no bits-ui (input is native <input> styled by token vars):

• Label — for, required/optional indicator
• Input — type (text/email/number/password/search), size, invalid state
• Field — wraps Label + Input + helper/error text (composition primitive)
• InputGroup — horizontal cluster (e.g. prefix + input + suffix)

Done when

• Each primitive has <Name>.svelte + index.ts barrel.
• shared/ui/index.ts re-exports all 4.
• npm run check passes.
• One commit on feature/issue-68-shadcn-components.

Parent: #68

[fedorovvvv]

Done in 66931ee. npm run check clean.