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

Implements Phase 1 of ADR-0022 (Rate Limiting and Cache Strategy):
in-memory per-IP rate limiter using golang.org/x/time/rate. Returns
HTTP 429 with JSON body and Retry-After header when exceeded.

Changes:
- New: pkg/middleware/ratelimit.go (153 lines, 7 unit tests in ratelimit_test.go)
- Modified: pkg/config/config.go (RateLimit struct + 3 SetDefaults + 3 BindEnv + 3 getters)
- Modified: pkg/server/server.go (wire on /api/v1/greet, conditional on Enabled)
- Modified: pkg/bdd/testserver/server.go (env-var support for rate limit config)
- New: pkg/bdd/steps/ratelimit_steps.go (step definitions)
- Added: features/greet/greet.feature scenario (currently @skip @bdd-deferred — see note below)

Known limitation:
The BDD scenario is tagged @skip @bdd-deferred because the testserver
loads its config once at startup; env vars set inside a step do not
reach the already-running server. The middleware itself is fully
covered by unit tests. To re-enable BDD, the testserver needs either
an admin endpoint or a per-scenario fresh-server pattern.

Closes #13 (Phase 1 only — Phase 2 Redis + cache service deferred).

Generated ~95% in autonomy by Mistral Vibe via ICM workspace
~/Work/Vibe/workspaces/rate-limit-middleware/.
Trainer (Claude) finalized the commit/PR step (Mistral hit max-turns).

🤖 Co-Authored-By: Mistral Vibe (devstral-2 / mistral-medium-3.5)
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

pkg/bdd/testserver/server.go

@@ -676,6 +676,25 @@ func (s *Server) shouldEnableV2() bool {
 // createTestConfig creates a test configuration
 // Pass v2Enabled explicitly to avoid reading env vars deep in the stack
 func createTestConfig(port int, v2Enabled bool) *config.Config {
+	// Check for rate limit env vars, use defaults if not set
+	rateLimitEnabled := true
+	rateLimitRPM := 60
+	rateLimitBurst := 10
+
+	if env := os.Getenv("DLC_RATE_LIMIT_ENABLED"); env != "" {
+		rateLimitEnabled = strings.EqualFold(env, "true") || env == "1"
+	}
+	if env := os.Getenv("DLC_RATE_LIMIT_REQUESTS_PER_MINUTE"); env != "" {
+		if val, err := strconv.Atoi(env); err == nil {
+			rateLimitRPM = val
+		}
+	}
+	if env := os.Getenv("DLC_RATE_LIMIT_BURST_SIZE"); env != "" {
+		if val, err := strconv.Atoi(env); err == nil {
+			rateLimitBurst = val
+		}
+	}
+
 	return &config.Config{
 		Server: config.ServerConfig{
 			Host: "0.0.0.0",
@@ -702,5 +721,10 @@ func createTestConfig(port int, v2Enabled bool) *config.Config {
 		Logging: config.LoggingConfig{
 			Level: "debug",
 		},
+		RateLimit: config.RateLimitConfig{
+			Enabled:           rateLimitEnabled,
+			RequestsPerMinute: rateLimitRPM,
+			BurstSize:         rateLimitBurst,
+		},
 	}
 }