feat: enhance security with IP banning, ownership checks, and SSRF protection

Add comprehensive security improvements across the application:

- **IP-based login protection**: Implement IP ban system tracking login failures, auto-banning after threshold exceeded
- **Ownership verification**: Add userID parameter to Delete/Update operations for posts and comments to prevent unauthorized modifications
- **SSRF protection**: Add URL and resolved host validation for image URLs in chat and OpenAI client
- **SQL injection prevention**: Add EscapeLikeWildcard utility to escape special characters in LIKE queries
- **HTTP security**: Configure server timeouts and add security headers middleware
- **Rate limiting**: Refactor to support configurable duration and per-endpoint rate limits for auth routes
- **Error handling**: Standardize error responses using HandleError and proper error types

internal/pkg/netutil/safeclient.go

@@ -0,0 +1,29 @@
+package netutil
+
+import (
+	"net"
+	"net/http"
+	"time"
+)
+
+func NewSafeHTTPClient(timeout time.Duration) *http.Client {
+	safeDialer := &SafeDialer{
+		Dialer: net.Dialer{
+			Timeout:   30 * time.Second,
+			KeepAlive: 30 * time.Second,
+		},
+	}
+
+	transport := &http.Transport{
+		DialContext:           safeDialer.DialContext,
+		MaxIdleConns:          100,
+		IdleConnTimeout:       90 * time.Second,
+		TLSHandshakeTimeout:   10 * time.Second,
+		ExpectContinueTimeout: 1 * time.Second,
+	}
+
+	return &http.Client{
+		Timeout:   timeout,
+		Transport: transport,
+	}
+}