feat: implement comprehensive thinking modes and migrate to google-genai

Major improvements to thinking capabilities and API integration:

- Remove all output token limits for future-proof responses
- Add 5-level thinking mode system: minimal, low, medium, high, max
- Migrate from google-generativeai to google-genai library
- Implement native thinkingBudget support for Gemini 2.5 Pro
- Set medium thinking as default for all tools, max for think_deeper

🧠 Thinking Modes:
- minimal (128 tokens) - simple tasks
- low (2048 tokens) - basic reasoning
- medium (8192 tokens) - default for most tools
- high (16384 tokens) - complex analysis
- max (32768 tokens) - default for think_deeper

🔧 Technical Changes:
- Complete migration to google-genai>=1.19.0
- Remove google-generativeai dependency
- Add ThinkingConfig with thinking_budget parameter
- Update all tools to support thinking_mode parameter
- Comprehensive test suite with 37 passing unit tests
- CI-friendly testing (no API key required for unit tests)
- Live integration tests for API verification

🧪 Testing & CI:
- Add GitHub Actions workflow with multi-Python support
- Unit tests use mocks, no API key required
- Live integration tests optional with API key
- Contributing guide with development setup
- All tests pass without external dependencies

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

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

tools/analyze.py

@@ -79,6 +79,11 @@ class AnalyzeTool(BaseTool):
                     "minimum": 0,
                     "maximum": 1,
                 },
+                "thinking_mode": {
+                    "type": "string",
+                    "enum": ["minimal", "low", "medium", "high", "max"],
+                    "description": "Thinking depth: minimal (128), low (2048), medium (8192), high (16384), max (32768)",
+                },
             },
             "required": ["files", "question"],
         }