fix: prioritize database provider configs and implement API key encryption

- Added AES-GCM encryption/decryption for provider API keys in the database.
- Implemented RefreshProviders to load provider configs from the database with precedence over environment variables.
- Updated dashboard handlers to encrypt keys on save and trigger in-memory provider refresh.
- Updated Grok test model to grok-3-mini for better compatibility.

internal/utils/crypto.go

@@ -0,0 +1,71 @@
+package utils
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"encoding/base64"
+	"fmt"
+	"io"
+)
+
+// Encrypt encrypts plain text using AES-GCM with the given 32-byte key.
+func Encrypt(plainText string, key []byte) (string, error) {
+	if len(key) != 32 {
+		return "", fmt.Errorf("encryption key must be 32 bytes")
+	}
+
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", err
+	}
+
+	nonce := make([]byte, gcm.NonceSize())
+	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
+		return "", err
+	}
+
+	// The nonce should be prepended to the ciphertext
+	cipherText := gcm.Seal(nonce, nonce, []byte(plainText), nil)
+	return base64.StdEncoding.EncodeToString(cipherText), nil
+}
+
+// Decrypt decrypts base64-encoded cipher text using AES-GCM with the given 32-byte key.
+func Decrypt(encodedCipherText string, key []byte) (string, error) {
+	if len(key) != 32 {
+		return "", fmt.Errorf("encryption key must be 32 bytes")
+	}
+
+	cipherText, err := base64.StdEncoding.DecodeString(encodedCipherText)
+	if err != nil {
+		return "", err
+	}
+
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return "", err
+	}
+
+	nonceSize := gcm.NonceSize()
+	if len(cipherText) < nonceSize {
+		return "", fmt.Errorf("cipher text too short")
+	}
+
+	nonce, actualCipherText := cipherText[:nonceSize], cipherText[nonceSize:]
+	plainText, err := gcm.Open(nil, nonce, actualCipherText, nil)
+	if err != nil {
+		return "", err
+	}
+
+	return string(plainText), nil
+}