feat: add quickstart command and modernize python scaffold

[Huerte]

Type

• Bug fix
• New feature
• Documentation
• Refactor / internal

Overview

Added a new gitgo new quickstart command that chains local scaffolding, remote repo creation, and pushing into a single step. The old new command was renamed to repo to clearly indicate it only creates the remote repository, also modernized the python scaffold to use pyproject.toml.

Closes #76

Changes

• gitgo repo: renamed from gitgo new to handle just the github remote creation.
• gitgo new: now acts as a quickstart command that executes init, repo, and link sequentially.
• init.py: updated the python scaffold to write pyproject.toml and .python-version instead of requirements.txt.
• link.py: extracted link_core and added a silent flag to suppress duplicate banners when called internally by the new command.
• CHANGELOG.md: documented the command additions and python scaffold changes.
• README.md: updated the content of readme due to new commands additions.

How to Test

1. pip install -e ".[dev]"
2. gitgo new test-app python --private
3. Expected result: A local folder test-app is created with a pyproject.toml, a private remote repo test-app is created on your github, the code is automatically committed and pushed, and the custom "PROJECT LAUNCHED" banner is printed.
4. pytest
5. Expected result: All 237 tests should run and pass successfully.

Checklist

• I tested my changes locally and they work
• I updated CHANGELOG.md under the [Unreleased] section
• I updated README.md (if I added or changed a command)
• I added or updated tests for my change (if applicable)
• My change does not break any existing commands (if it does, describe the impact in the Overview)