Export AssemblyInstructionsInput type from @uppy/transloadit (#6184)

The `AssemblyInstructionsInput` type from `@transloadit/types` is now
publicly exported from `@uppy/transloadit`, allowing consumers to type
their assembly parameters without importing from the external package.

## Changes

- Re-exported `AssemblyInstructionsInput` type in
`packages/@uppy/transloadit/src/index.ts`

## Usage

```typescript
import type { AssemblyInstructionsInput } from '@uppy/transloadit'

const params: AssemblyInstructionsInput = {
  steps: {
    encode: {
      robot: '/video/encode',
      use: ':original',
      preset: 'mp4',
    },
  },
}
```

The type was already imported internally and aliased as
`AssemblyParameters`. This change makes it available to plugin
consumers.

<!-- START COPILOT ORIGINAL PROMPT -->



<details>

<summary>Original prompt</summary>

> Make the AssemblyInstructionsInput type available from the
@uppy/transloadit package by re-exporting it from
packages/@uppy/transloadit/src/index.ts.
> 
> Background
> - The Transloadit plugin imports the type AssemblyInstructionsInput
from the external package @transloadit/types and aliases it as
AssemblyParameters in packages/@uppy/transloadit/src/index.ts.
> - Consumers of the @uppy/transloadit package need direct access to the
AssemblyInstructionsInput type but it is not currently exported from the
plugin package.
> 
> Change requested
> - Add a type re-export so that consumers can import
AssemblyInstructionsInput from the transloadit plugin package, e.g.
>   import type { AssemblyInstructionsInput } from '@uppy/transloadit'
> 
> Files to change
> - packages/@uppy/transloadit/src/index.ts
> - Add the following export alongside the other package exports (near
the end of the module where other exports live):
> 
> ```typescript name=packages/@uppy/transloadit/src/index.ts
url=https://github.com/transloadit/uppy/blob/main/packages/@uppy/transloadit/src/index.ts
> -export { COMPANION_URL, COMPANION_ALLOWED_HOSTS }
> +export { COMPANION_URL, COMPANION_ALLOWED_HOSTS }
> +
> +// Re-export type from @transloadit/types so callers can import it
from the plugin package.
> +export type { AssemblyInstructionsInput } from '@transloadit/types'
> ```
> 
> Notes
> - This is a purely type-only export and should be erased at compile
time; it does not add runtime code.
> - No other behavior or API surface should change.
> 
> Please create a branch, apply the change, and open a pull request with
a descriptive title and a short description of the change. Run
TypeScript build checks if available.
> 


</details>



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.changeset/clever-crabs-worry.md

@@ -0,0 +1,5 @@
+---
+"@uppy/transloadit": patch
+---
+
+Add type re-export for `AssemblyInstructionsInput`

packages/@uppy/transloadit/src/index.ts

@@ -1050,6 +1050,9 @@ export default class Transloadit<
 
 export { COMPANION_URL, COMPANION_ALLOWED_HOSTS }
 
+// Re-export type from @transloadit/types so callers can import it from the plugin package.
+export type { AssemblyInstructionsInput } from '@transloadit/types'
+
 // Low-level classes for advanced usage (e.g., creating assemblies without file uploads)
 export { default as Assembly } from './Assembly.js'
 export { AssemblyError, default as Client } from './Client.js'