feat: Add input validation and type hints for CodeRabbit review

- Add validation for empty messages list
- Add temperature range validation (0-2)
- Add max_tokens minimum validation
- Improve type hints with return type annotations
- Better error messages for validation failures
- Add CodeRabbit configuration file

Testing CodeRabbit integration.

CODERABBIT_SETUP.md

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+# CodeRabbit Setup Troubleshooting
+
+## Issue: CodeRabbit not appearing in PRs
+
+### Step 1: Verify Installation
+
+1. Go to: https://github.com/marketplace/coderabbitai
+2. Click "Install it for free" or "Configure access"
+3. Make sure it's installed for your organization/user
+4. Verify it has access to `DealExMachina/simple-llm-pro-finance`
+
+### Step 2: Check Repository Settings
+
+1. Go to: https://github.com/DealExMachina/simple-llm-pro-finance/settings/installations
+2. Look for "CodeRabbitAI" in installed GitHub Apps
+3. Click "Configure" next to it
+4. Ensure this repository is selected (or "All repositories")
+
+### Step 3: Check Webhooks
+
+1. Go to: https://github.com/DealExMachina/simple-llm-pro-finance/settings/hooks
+2. Look for a webhook pointing to: `https://app.coderabbit.ai/githubHandler`
+3. If missing, CodeRabbit should create it automatically, but you can check
+
+### Step 4: Test with a Real PR
+
+CodeRabbit may need:
+- **Code changes** (not just docs)
+- **Multiple files** changed
+- **Python files** to review
+
+Try this:
+
+```bash
+# Create a test PR with actual code changes
+git checkout -b test-coderabbit-code
+# Make a small code change (add a comment, fix formatting)
+# Then create PR
+```
+
+### Step 5: Check PR for CodeRabbit Bot
+
+- Look for user: `@coderabbitai` or `@coderabbit`
+- Check "Conversation" tab in PR
+- Sometimes it takes 2-5 minutes to appear
+
+### Step 6: Manual Trigger
+
+Try adding this to your PR description:
+```
+@coderabbitai please review
+```
+
+Or mention it:
+```
+@coderabbit please review this PR
+```
+
+### Step 7: Verify Configuration File
+
+The `.coderabbit.yaml` file has been created. CodeRabbit should respect this configuration.
+
+### Alternative: Use CodeRabbit Comments
+
+If CodeRabbit is installed but not auto-commenting, try:
+1. Comment in the PR: `/review` or `/review_code`
+2. Or use: `/ask @coderabbitai review this PR`
+
+## Still Not Working?
+
+1. Check CodeRabbit status: https://status.coderabbit.ai/
+2. Review CodeRabbit docs: https://docs.coderabbit.ai/
+3. Contact support: https://coderabbit.ai/support
+
+## What CodeRabbit Should Review:
+
+- Code quality and best practices
+- Security vulnerabilities
+- Performance issues
+- Python-specific patterns
+- Error handling
+- Documentation completeness
+

CODERABBIT_TEST_PR.md

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+# CodeRabbit Test PR - Code Changes
+
+This PR includes intentional code changes that CodeRabbit should review:
+
+## Changes Made:
+1. Added input validation to chat completions endpoint
+2. Improved error handling with better error messages
+3. Added type hints improvements
+
+## What CodeRabbit Should Catch:
+- Code quality improvements
+- Potential security issues
+- Best practices suggestions
+- Python typing improvements
+