Add Support for uvx gito.bot

[marutichintan]

This pull request introduces improved handling of invalid environment variable values for LLM_API_PLATFORM, updates documentation to clarify installation via uvx, and adds tests for the new environment sanitization logic. The most important changes are as follows:

Environment variable sanitization:

• Added _sanitize_env_vars and _sanitized_home_env_path functions to gito/bootstrap.py to ignore or remove invalid sentinel values (such as "none" or "null") for LLM_API_PLATFORM from both the shell environment and .env files. This prevents misconfiguration due to placeholder values. [1] [2]
• Updated the bootstrap function to use the sanitized environment variables and .env file path during application startup.

Testing:

• Added tests in tests/test_bootstrap.py to verify that invalid LLM_API_PLATFORM values are properly removed from both the environment and .env files, and that valid values are preserved.

Documentation improvements:

• Updated the installation instructions in README.md to clarify the use of uvx for running Gito without a global install, and explained the difference between the package name (gito.bot) and the CLI executable (gito).
• Added troubleshooting guidance in documentation/troubleshooting.md for users who might accidentally install the wrong package with uvx, including correct usage examples.

[Nayjest]

Thanks @marutichintan

[Nayjest]

#256

[Nayjest]

uvx fix was released here:
https://github.com/Nayjest/Gito/releases/tag/v4.0.4

@marutichintan
I would appreciate if you can shortly describe steps to reproduce the issue with LLM_API_PLATFORM