fix: remove space in FATAL match and use project_root for .env path

[PrinceGautam2106]

1. Problem

Fixes two bugs: FATAL log lines without surrounding spaces were not
colorized red, and the .env file was saved to the current working
directory instead of the project root.

2. Changes

• crates/mofa-cli/src/commands/agent/logs.rs: Removed extra space
  inside " FATAL" string so FATAL: prefixed lines are correctly
  colorized red
• mofa/commands/vibe.py: Changed os.getcwd() to project_root so
  .env is always saved in the correct project location

[PrinceGautam2106]

Hello @lijingrs @yangrudan
This fixes two small bugs found in the codebase — removing an extra space in the FATAL match string so fatal log lines are correctly colorized red, and replacing os.getcwd() with project_root so the .env file saves to the correct location. Minimal changes, no behavior shift elsewhere, and a test added for the Rust fix.