Add uv-powered quick start path for end-to-end runs

[vecnode]

Introduce a single uv-driven command (for example, a make target or script) that installs dependencies and executes a canonical text‑to‑image run in one step, optimized for a fresh machine.

Why

• New users benefit from a “one command” path to see the system working end‑to‑end.
• A single optimized bootstrap path helps catch regressions in setup and runtime in CI.
• Using uv run keeps environment management fast and consistent with the rest of the repo.

What to do

• Define a standard “quick start” scenario (e.g., text‑to‑image with a simple prompt and default model).
• Add a script or Make target that:
  • Ensures dependencies are installed via uv.
  • Downloads any required models/assets if missing.
  • Runs the standard scenario and writes outputs to a known location.
• Wire this script into the README as the recommended first command for new users.
• Optionally add a CI job that runs this quick start to validate the full stack.

Acceptance criteria

• A single documented command (e.g., make quickstart or uv run scripts/quickstart.py) can be executed on a clean machine to produce an example output.
• The command is idempotent and safe to re‑run (reuses env, cached models, etc.).
• No behavior changes for advanced workflows; this is an additive, guided path.