Generated .gitignore missing .venv/ causes virtual environment to be committed

[notgitika]

Description

The gitignore templates for all 6 Python frameworks are missing .venv/, the default directory created by python -m venv .venv. This causes hundreds of MB of third-party packages to be staged on git add .. Additionally, the Strands template has a duplicate .env entry.

Steps to Reproduce

1. agentcore create with any Python framework
2. python -m venv .venv in the agent directory
3. git add .
4. git status shows .venv/ contents staged

Expected Behavior

.venv/ should be in .gitignore and excluded from staging.

Actual Behavior

.venv/ is not in .gitignore, so the entire virtual environment (hundreds of MB) gets staged for commit.

Operating System

macOS