Use build args for git user config

Change git configuration to use Docker build args instead of .env file,
simplifying setup and improving security. This change:
- Removes git config from .env and startup.sh
- Adds GIT_USER_NAME and GIT_USER_EMAIL build args
- Updates documentation for new git config approach
- Improves task logging requirements in CLAUDE.md

The build arg approach provides better isolation and ensures git config is
properly set during image build rather than container runtime.

.env.example

@@ -1,10 +1,6 @@
 # Copy this file to .env and fill in your credentials
 # The .env file will be baked into the Docker image during build
 
-# Required: Git configuration for commits made inside the container
-GIT_USER_NAME=Your Name
-GIT_USER_EMAIL=your.email@example.com
-
 # Optional: Twilio credentials for SMS notifications
 TWILIO_ACCOUNT_SID=your_twilio_account_sid
 TWILIO_AUTH_TOKEN=your_twilio_auth_token