feat(backend): update rate limiting middleware

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

backend/mw/ratelimit_dev.go

@@ -5,6 +5,7 @@ package mw
 
 import (
 	"net/http"
+	"sync"
 	"time"
 )
 
@@ -15,3 +16,29 @@ func RateLimit(limit int, window time.Duration) func(http.Handler) http.Handler
 		})
 	}
 }
+
+type ProgressiveRateLimiter struct {
+	requests map[string]*ipProgressiveState
+	mu       sync.RWMutex
+}
+
+type ipProgressiveState struct {
+	timestamps []time.Time
+}
+
+func NewProgressiveRateLimiter() *ProgressiveRateLimiter {
+	return &ProgressiveRateLimiter{
+		requests: make(map[string]*ipProgressiveState),
+	}
+}
+
+func (prl *ProgressiveRateLimiter) cleanup() {}
+func (prl *ProgressiveRateLimiter) Check(ip string) int { return 0 }
+
+var globalProgressiveLimiter = NewProgressiveRateLimiter()
+
+func ProgressiveRateLimit(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		next.ServeHTTP(w, r)
+	})
+}