✨ feat(server): add per-IP rate limit middleware on /api/v1/greet (#22)

Phase 1 of ADR-0022. In-memory per-IP rate limiter on golang.org/x/time/rate. Returns 429 with Retry-After when exceeded. 7 unit tests pass. BDD scenario @skip until testserver rework. Closes #13.

~95% Mistral Vibe autonomous via ICM workspace. Cost ~6.5€ (T5 + resume + trainer commit/PR).

Co-authored-by: Gabriel Radureau <arcodange@gmail.com>
Co-committed-by: Gabriel Radureau <arcodange@gmail.com>

pkg/bdd/steps/steps.go

@@ -16,6 +16,7 @@ type StepContext struct {
 	commonSteps       *CommonSteps
 	jwtRetentionSteps *JWTRetentionSteps
 	configSteps       *ConfigSteps
+	rateLimitSteps    *RateLimitSteps
 }
 
 // NewStepContext creates a new step context
@@ -28,6 +29,7 @@ func NewStepContext(client *testserver.Client) *StepContext {
 		commonSteps:       NewCommonSteps(client),
 		jwtRetentionSteps: NewJWTRetentionSteps(client),
 		configSteps:       NewConfigSteps(client),
+		rateLimitSteps:    NewRateLimitSteps(client),
 	}
 }
 
@@ -62,6 +64,9 @@ func SetScenarioKeyForAllSteps(sc *StepContext, key string) {
 		if sc.commonSteps != nil {
 			sc.commonSteps.SetScenarioKey(key)
 		}
+		if sc.rateLimitSteps != nil {
+			sc.rateLimitSteps.SetScenarioKey(key)
+		}
 	}
 }
 
@@ -294,6 +299,15 @@ func InitializeAllSteps(ctx *godog.ScenarioContext, client *testserver.Client, s
 	ctx.Step(`^the audit entry should contain the previous and new values$`, sc.configSteps.theAuditEntryShouldContainThePreviousAndNewValues)
 	ctx.Step(`^the audit entry should contain the timestamp of the change$`, sc.configSteps.theAuditEntryShouldContainTheTimestampOfTheChange)
 
+	// Rate limit steps
+	ctx.Step(`^the server is running with rate limit set to (\d+) requests per minute and burst (\d+)$`, sc.rateLimitSteps.theServerIsRunningWithRateLimitSetTo)
+	ctx.Step(`^I make (\d+) requests to "([^"]*)"$`, sc.rateLimitSteps.iMakeNRequestsTo)
+	ctx.Step(`^all responses should have status (\d+)$`, sc.rateLimitSteps.allResponsesShouldHaveStatus)
+	ctx.Step(`^I make 1 more request to "([^"]*)"$`, sc.rateLimitSteps.iMakeOneMoreRequestTo)
+	ctx.Step(`^the response should have status (\d+)$`, sc.rateLimitSteps.theResponseShouldHaveStatus)
+	ctx.Step(`^the response body should contain "([^"]*)"$`, sc.rateLimitSteps.theResponseBodyShouldContain)
+	ctx.Step(`^the response should have header "([^"]*)"$`, sc.rateLimitSteps.theResponseShouldHaveHeader)
+
 	// Common steps
 	ctx.Step(`^the response should be "{\\"([^"]*)":\\"([^"]*)"}"$`, sc.commonSteps.theResponseShouldBe)
 	ctx.Step(`^the response should contain error "([^"]*)"$`, sc.commonSteps.theResponseShouldContainError)