feat: add persistent profile storage to ~/.kvs/config.json

Implemented roadmap #1: Configuration file for persistent profiles.

Features:
- Auto-saves profiles to ~/.kvs/config.json on add/use/remove
- Auto-loads profiles on shell startup
- File created with 0600 permissions for token security
- Shows active profile in welcome message
- Added 'profile save' and 'profile load' commands for manual control

Technical details:
- Created config.go with LoadConfig/SaveConfig functions
- Profile changes automatically trigger persistence
- ~/.kvs directory created with 0700 permissions if missing
- Gracefully handles missing config file on first run

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

cmd_profile.go

@@ -38,6 +38,7 @@ func (c *KVSClient) handleProfile(args []string) {
 			BaseURL:  baseURL,
 		}
 		fmt.Println(green("Profile added:"), args[1])
+		c.saveProfiles()
 
 	case "use":
 		if len(args) < 2 {
@@ -54,6 +55,7 @@ func (c *KVSClient) handleProfile(args []string) {
 		c.baseURL = profile.BaseURL
 		c.activeProfile = args[1]
 		fmt.Println(green("Switched to profile:"), args[1])
+		c.saveProfiles()
 
 	case "remove":
 		if len(args) < 2 {
@@ -65,5 +67,29 @@ func (c *KVSClient) handleProfile(args []string) {
 			c.activeProfile = ""
 		}
 		fmt.Println(green("Profile removed:"), args[1])
+		c.saveProfiles()
+
+	case "save":
+		if err := c.saveProfiles(); err != nil {
+			fmt.Println(red("Error saving profiles:"), err)
+			return
+		}
+		fmt.Println(green("Profiles saved to ~/.kvs/config.json"))
+
+	case "load":
+		config, err := LoadConfig()
+		if err != nil {
+			fmt.Println(red("Error loading profiles:"), err)
+			return
+		}
+		c.syncConfigToClient(config)
+		fmt.Println(green("Profiles loaded from ~/.kvs/config.json"))
+		if c.activeProfile != "" {
+			fmt.Println(cyan("Active profile:"), c.activeProfile)
+		}
+
+	default:
+		fmt.Println(red("Unknown profile command:"), subCmd)
+		fmt.Println("Available commands: add, use, remove, save, load")
 	}
 }