feat(cli): unified headless CLI for creative execution and system management (M8)

[BerryUIKI]

Summary

This PR implements Milestone M8: Unified Berry CLI for creation, task management, and environment supervision, sharing the exact same backend services as the GUI workspace.

Key Capabilities

• Creative Execution (\�erry run): Supports text-to-image, image-to-image, inpainting, upscaling, text-to-video, and image-to-video actions. Features automatic local file base64 uploading, deterministic dirty-check caching, and automatic output download (--output).
• Task Management (\�erry tasks): Inspect in-flight generation tasks (\�erry tasks list) and safely dispatch cancellation tokens (\�erry tasks cancel ).
• Diagnostics (\�erry system): Query hardware readiness, GPU platform status, and running engine endpoints.
• Scriptability (--json): All commands support structured machine-readable JSON output for shell scripting and automation.
• Reference Documentation: Added comprehensive reference in \docs/CLI_REFERENCE.md.

Automated Verification

• Backend pytest: 83 passed (including new \�ackend/tests/test_m8_cli.py)
• Launcher tests: 2 passed (flag parsing, zero-dependency base64 encoder)
• Frontend build: TypeScript typecheck and Vite build passed cleanly