Add InputGroup component with alignment variants and sub-components

[Copilot]

The codebase was missing a composable InputGroup UI component for building styled input layouts with addons, buttons, and text decorators.

Component: client/src/components/ui/input-group.tsx

Six exported sub-components following shadcn/ui patterns:

• InputGroup — Flex container managing shared border, focus ring, and error ring via CSS has-[] selectors. Supports inline and block alignment layouts automatically.
• InputGroupAddon — cva-powered wrapper with 4 alignment variants (inline-start, inline-end, block-start, block-end). Auto-focuses nested <input> on click.
• InputGroupButton — Shadow-free Button with compact sizes (xs, sm, icon-xs, icon-sm) for in-group actions.
• InputGroupText — Semantic <span> for static labels or icons.
• InputGroupInput — Input wrapper with data-slot="input-group-control" that removes duplicate borders/shadows/focus rings (delegated to parent InputGroup).
• InputGroupTextarea — Same as InputGroupInput with resize disabled and vertical padding.

<InputGroup>
  <InputGroupAddon align="inline-start">
    <SearchIcon />
  </InputGroupAddon>
  <InputGroupInput placeholder="Search..." />
  <InputGroupAddon align="inline-end">
    <InputGroupButton><XIcon /></InputGroupButton>
  </InputGroupAddon>
</InputGroup>

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