fix: [#257] Resolve profile execute to cwd instead of package install dir

[hendo-21]

Description

Fixes #257.

• Resolves the template path used by profile.execute() against cwd instead of Path(__file__).resolve().parents[1] (the package install dir), so it can locate templates pulled via fenn pull.
• Removes the template.parent != ROOT guard to allow profiling of templates nested within cwd.
• Updates test_profile_execute_generates_profile_and_report to parametrize over flat and nested templates; retains original coverage for the non-nested case.
• Adds a regression test verifying profile.execute() raises SystemExit(1) for a template dir missing main.py.

Verification

• Ran the entire test suite: all passing.
• Pre-commit checks: all passing.

[ApusBerliozi]

Thx 4 your effort @hendo-21 !