chore(claude): remove dotcms-frontend-review skill and exclusive agents

[oidacra]

Description

Remove the .claude/skills/dotcms-frontend-review/ skill and its two exclusive agents (dotcms-code-reviewer, dotcms-test-reviewer) from the repository. These agents are not referenced by any other skill and the skill itself is no longer in use. Also add .venv/ to .gitignore so local Python virtualenvs are not tracked.

Tracked by PR: #35400

Acceptance Criteria

• .claude/skills/dotcms-frontend-review/ directory is removed
• dotcms-code-reviewer agent is removed
• dotcms-test-reviewer agent is removed
• No remaining references: git grep -E "dotcms-(frontend-review|code-reviewer|test-reviewer)" returns empty
• .venv/ is added to .gitignore

Additional Context

Quick draft — details to be refined if needed. Implementation is already in PR #35400.