feat: add spacy model to env.go

[marcpfuller]

Add spacy model configuration support for multi-language passive voice detection

Adds configuration support for the SPACY_MODEL environment variable to enable multi-language passive voice detection in Ghostwriter.

Changes

• Added spacy_model default configuration (en_core_web_sm) in setGhostwriterConfigDefaultValues()
• Added spacy alias for convenience access to spacy_model setting

Usage

# View current model
ghostwriter-cli config get spacy_model

# Change to a different language model
ghostwriter-cli config set spacy_model de_core_news_sm

# Using alias
ghostwriter-cli config get spacy
ghostwriter-cli config set spacy fr_core_news_sm