Implementing Ui Bundle File Upload

# File Upload API (workflow)

When the user wants file upload functionality in a React UI bundle, follow this workflow. This feature provides **APIs only** — you must build the UI components yourself using the provided APIs.

## CRITICAL: This is an API-only package

The package exports **programmatic APIs**, not React components or hooks. You will:

- Use the `upload()` function to handle file uploads with progress tracking
- Build your own custom UI (file input, dropzone, progress bars, etc.)
- Track upload progress through the `onProgress` callback

**Do NOT:**

- Expect pre-built components like `<FileUpload />` — they are not exported
- Try to import React hooks like `useFileUpload` — they are not exported
- Look for dropzone components — they are not exported

The source code contains reference components for demonstration, but they are **not available** as imports. Use them as examples to build your own UI.

## 1. Install the package

```bash
npm install @salesforce/ui-bundle-template-feature-react-file-upload
```

Dependencies are automatically installed:

- `@salesforce/ui-bundle` (API client)
- `@salesforce/sdk-data` (data SDK)

## 2. Understand the three upload patterns

### Pattern A: Basic upload (no record linking)

Upload files to Salesforce and get back `contentBodyId` for each file. No ContentVersion record is created.

**When to use:**

- User wants to upload files first, then create/link them to a record later
- Building a multi-step form where the record doesn't exist yet
- Deferred record linking scenarios

```tsx
import { upload } from "@salesforce/ui-bundle-template-feature-react-file-upload";

const results = await upload({
  files: [file1, file2],
  onProgress: (progress) => {
    console.log(`${progress.fileName}: ${progress.status} - ${progress.progress}%`);
  },
});

// results[0].contentBodyId: "069..." (always available)
// results[0].contentVersionId: undefined (no record linked)
```

### Pattern B: Upload with immediate record linking

Upload files and immediately link them to an existing Salesforce record by creating ContentVersion records.

**When to use:**

- Record already exists (Account, Opportunity, Case, etc.)
- User wants files immediately attached to the record
- Direct upload-and-attach scenarios

```tsx
import { upload } from "@salesforce/ui-bundle-template-feature-react-file-upload";

const results = await upload({
  files: [file1, file2],
  recordId: "001xx000000yyyy", // Existing record ID
  onProgress: (progress) => {
    console.log(`${progress.fileName}: ${progress.status} - ${progress.progress}%`);
  },
});

// results[0].contentBodyId: "069..." (always available)
// results[0].contentVersionId: "068..." (linked to record)
```

### Pattern C: Deferred record linking (record creation flow)

Upload files without a record, then link them after the record is created.

**When to use:**

- Building a "create record with attachments" form
- Record doesn't exist until form submission
- Need to upload files before knowing the final record ID

```tsx
import {
  upload,
  createContentVersion,
} from "@salesforce/ui-bundle-template-feature-react-file-upload";

// Step 1: Upload files (no recordId)
const uploadResults = await upload({
  files: [file1, file2],
  onProgress: (progress) => console.log(progress),
});

// Step 2: Create the record
const newRecordId = await createRecord(formData);

// Step 3: Link uploaded files to the new record
for (const file of up