feat: Add .env.template and update .gitignore

Introduces a comprehensive .env.template file to guide users in configuring environment variables for the Personal Assistant AI. This template includes sections for AI, database, external services, admin, security, application, Redis, email, file upload, and monitoring configurations.

Updates .gitignore to explicitly ignore various local .env files while ensuring .env.template and .env.example are not ignored, facilitating proper distribution and usage.

Also updates PUBLIC_RELEASE_SUMMARY.md to reflect the inclusion of .env.template.