style: fix linting and formatting issues

- Run black formatter on all Python files
- Fix ruff linting issues:
  - Remove unused imports
  - Remove unused variables
  - Fix f-string without placeholders
- All 37 tests still pass
- Code quality improved for CI/CD compliance

🧹 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

prompts/__init__.py

@@ -2,8 +2,13 @@
 System prompts for Gemini tools
 """
 
-from .tool_prompts import (ANALYZE_PROMPT, CHAT_PROMPT, DEBUG_ISSUE_PROMPT,
-                           REVIEW_CODE_PROMPT, THINK_DEEPER_PROMPT)
+from .tool_prompts import (
+    ANALYZE_PROMPT,
+    CHAT_PROMPT,
+    DEBUG_ISSUE_PROMPT,
+    REVIEW_CODE_PROMPT,
+    THINK_DEEPER_PROMPT,
+)
 
 __all__ = [
     "THINK_DEEPER_PROMPT",