feat: implement BDD testing with Godog

Implement comprehensive BDD testing framework using Godog:
- Added feature files for greet and health endpoints
- Created test server that runs on port 9191
- Implemented step definitions using Godog's exact patterns
- Fixed undefined step warnings by following Godog conventions
- All tests passing with proper response validation
- Maintained black box testing principles

Key files:
- pkg/bdd/steps/steps.go - Step definitions using StepContext struct
- pkg/bdd/testserver/ - Test server implementation
- features/*.feature - BDD feature files
- pkg/bdd/README.md - Documentation for proper step patterns

The implementation follows Godog's exact pattern suggestions to avoid
undefined step warnings and provides comprehensive API testing.

pkg/bdd/README.md

@@ -0,0 +1,96 @@
+# BDD Testing with Godog
+
+This package implements Behavior-Driven Development (BDD) testing using the Godog framework.
+
+## Important Requirements for Step Definitions
+
+### Step Pattern Matching
+
+Godog has **very specific requirements** for step pattern matching. To avoid "undefined" warnings:
+
+1. **Use the exact regex pattern** that Godog suggests in its error messages
+2. **Use the exact parameter names** that Godog suggests (`arg1, arg2`, etc.)
+3. **Match the feature file syntax exactly** including quotes and JSON formatting
+
+### Example
+
+**Feature file step:**
+```gherkin
+Then the response should be "{\"message\":\"Hello world!\"}"
+```
+
+**Correct step definition:**
+```go
+ctx.Step(`^the response should be "{\"([^"]*)\":\"([^"]*)\"}"$`, func(arg1, arg2 string) error {
+    // Implementation here
+    return nil
+})
+```
+
+**Incorrect patterns that cause "undefined" warnings:**
+```go
+// Wrong: Different regex pattern
+ctx.Step(`^the response should be "{\"message\":\"([^"]*)\"}"$`, func(message string) error {
+    // ...
+})
+
+// Wrong: Different parameter names
+ctx.Step(`^the response should be "{\"([^"]*)\":\"([^"]*)\"}"$`, func(key, value string) error {
+    // ...
+})
+```
+
+## Current Implementation
+
+### Step Definition Strategy
+
+1. **First eliminate "undefined" warnings** by using Godog's exact suggested patterns
+2. **Return `godog.ErrPending`** initially to confirm pattern matching works
+3. **Then implement actual validation** logic
+
+### Files
+
+- `suite.go`: Test suite initialization and server management
+- `testserver/`: Test server and client implementation
+- `steps/`: Step definitions for each feature
+
+## Debugging "Undefined" Steps
+
+If you see "undefined" warnings:
+
+1. Run the tests to see Godog's suggested pattern:
+   ```bash
+   go test ./features/... -v
+   ```
+
+2. Copy the **exact regex pattern** from the error message
+3. Copy the **exact parameter names** (`arg1, arg2`, etc.)
+4. Update your step definition to match exactly
+
+## Common Mistakes
+
+The "undefined" warnings are **not a Godog bug** - they occur when step definitions don't match Godog's expected patterns exactly:
+
+- Using different regex patterns than what Godog suggests
+- Using descriptive parameter names instead of `arg1, arg2`
+- Not escaping quotes properly in JSON patterns
+- Trying to be "clever" with regex optimization
+
+**Solution**: Always use the exact pattern and parameter names that Godog suggests in its error messages.
+
+## Best Practices
+
+1. **Follow Godog's suggestions exactly** - Copy-paste the pattern and parameter names
+2. **Test pattern matching first** - Use `godog.ErrPending` to verify patterns work
+3. **Then implement logic** - Replace `godog.ErrPending` with actual validation
+4. **Don't over-optimize regex** - Use the patterns Godog provides, even if they seem verbose
+5. **One pattern per step type** - Use generic patterns to cover similar steps
+
+## Why This Matters
+
+Godog's step matching is **very specific by design**:
+- It needs to reliably match feature file steps to code
+- It provides exact patterns to ensure consistency
+- Following its suggestions guarantees your steps will be recognized
+
+**Remember**: The "undefined" warnings are Godog telling you exactly how to fix your step definitions!