feat: add batch upload example

[eren-karakus0]

Summary

Adds a new example app (apps/batch-upload) that demonstrates how to upload multiple files to Shelby in a single run. This addresses a common use case requested by the community (see shelby/feedback#14).

Features:

• Scans a directory and uploads all files sequentially
• Per-file error handling — one failure doesn't stop the rest
• Automatic duplicate detection — skips blobs that already exist
• File size display and upload summary with success/fail counts
• Configurable blob prefix and TTL

Structure

apps/batch-upload/
├── .env.example
├── assets/
│   ├── hello.txt
│   └── sample.json
├── package.json
├── README.md
├── src/
│   └── index.ts
└── tsconfig.json

Follows the same patterns and conventions as existing examples (upload-blob, download-blob, list-blob).

Test plan

• Biome lint passes (npx @biomejs/biome check apps/batch-upload/)
• Code follows existing example conventions (same deps, tsconfig, script structure)
• README includes prerequisites, setup, usage, example output, and troubleshooting

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Note

Low Risk
Adds a standalone example app and documentation without changing core SDK or production logic; main risk is minor maintenance drift as APIs evolve.

Overview
Adds a new example app, apps/batch-upload, showing how to batch upload multiple local files to Shelby in one run.

The script scans assets/, uploads files sequentially with configurable TTL/prefix, reports per-file progress and a final success/fail count, and skips uploads when the blob already exists (via EBLOB_WRITE_CHUNKSET_ALREADY_EXISTS). Includes a runnable pnpm upload setup with .env.example, sample assets, TypeScript config, and a README covering setup/usage/troubleshooting.

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