✨ Enhance unpack scripts with uv auto-setup, venv reuse, and interactive python discovery

[entr0pia]

...ractive python discovery

Description

This PR significantly improves the installation experience and performance of the offline bundles generated by uv-pack. Key enhancements include:

1. Automatic uv Integration: Bundles the uv wheel into the wheels/ directory during packing. The unpack scripts now detect if uv is missing and
   automatically install it from the bundled wheel to enable high-speed installation in air-gapped environments.
2. High-Performance Unpacking: Both unpack.sh and unpack.ps1 prioritize uv venv and uv pip install over legacy venv/pip when uv is available, drastically
   reducing deployment time.
3. Interactive Python Discovery: If the Python bundling step is skipped and BASE_PY is not provided, the scripts will search for available system Python
   interpreters and interactively prompt the user for confirmation (defaulting to Y).
4. Virtual Environment Reuse: Added a check for existing virtual environment directories. If a venv already exists, the script skips the creation step
   and proceeds directly to dependency synchronization.
5. Documentation Alignment: Updated the root README.md, the internal script documentation, and SPEC.md to ensure all technical specifications and user
   guides match the new implementation.

Related Issue

N/A

Type of Change

• 🔧 Bug fix
• 🔐 Security fix
• 🚀 Improvement / New feature
• 📚 Examples / Docs / Tutorials

Checklist

• I've checked the code using task check.
• I've checked the repository using pre-commit.

[davnn]

Hi, thanks for your contribution! I would like to gather some community feedback on this PR. This PR assumes that everyone wants to use uv for deployment, right? I currently prefer not to use uv in the deployment by default.

Should deployment with uv be the new default?
Should deployment without uv still be possible?
Should we add a CLI-option to enable/disable uv deployment?

[entr0pia]

I've updated the PR to make uv bundling optional during the packing phase (disabled by default). The unpacking scripts now follow a progressive enhancement strategy: they will still prioritize using uv (system-installed or bundled) if available for faster deployment, but will gracefully fallback to standard pip/venv if uv is not found. This ensures a 'clean' default while keeping the performance benefits accessible.