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>

config.go

@@ -0,0 +1,120 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+// Config holds the persistent configuration
+type Config struct {
+	Profiles      map[string]Profile `json:"profiles"`
+	ActiveProfile string             `json:"active_profile"`
+}
+
+// getConfigPath returns the path to the config file
+func getConfigPath() (string, error) {
+	homeDir, err := os.UserHomeDir()
+	if err != nil {
+		return "", err
+	}
+
+	kvsDir := filepath.Join(homeDir, ".kvs")
+	// Create .kvs directory if it doesn't exist
+	if err := os.MkdirAll(kvsDir, 0700); err != nil {
+		return "", err
+	}
+
+	return filepath.Join(kvsDir, "config.json"), nil
+}
+
+// LoadConfig loads the configuration from disk
+func LoadConfig() (*Config, error) {
+	configPath, err := getConfigPath()
+	if err != nil {
+		return nil, err
+	}
+
+	// If config doesn't exist, return empty config
+	if _, err := os.Stat(configPath); os.IsNotExist(err) {
+		return &Config{
+			Profiles: make(map[string]Profile),
+		}, nil
+	}
+
+	data, err := os.ReadFile(configPath)
+	if err != nil {
+		return nil, err
+	}
+
+	var config Config
+	if err := json.Unmarshal(data, &config); err != nil {
+		return nil, err
+	}
+
+	if config.Profiles == nil {
+		config.Profiles = make(map[string]Profile)
+	}
+
+	return &config, nil
+}
+
+// SaveConfig saves the configuration to disk with 0600 permissions
+func SaveConfig(config *Config) error {
+	configPath, err := getConfigPath()
+	if err != nil {
+		return err
+	}
+
+	data, err := json.MarshalIndent(config, "", "  ")
+	if err != nil {
+		return err
+	}
+
+	// Write with restrictive permissions (0600) to protect tokens
+	if err := os.WriteFile(configPath, data, 0600); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// syncConfigToClient updates client state from config
+func (c *KVSClient) syncConfigToClient(config *Config) {
+	c.profiles = config.Profiles
+	c.activeProfile = config.ActiveProfile
+
+	// If there's an active profile, apply it
+	if c.activeProfile != "" {
+		if profile, ok := c.profiles[c.activeProfile]; ok {
+			c.currentToken = profile.Token
+			c.currentUser = profile.UserUUID
+			c.baseURL = profile.BaseURL
+		}
+	}
+}
+
+// syncClientToConfig updates config from client state
+func (c *KVSClient) syncClientToConfig(config *Config) {
+	config.Profiles = c.profiles
+	config.ActiveProfile = c.activeProfile
+}
+
+// saveProfiles is a convenience method to save current client state
+func (c *KVSClient) saveProfiles() error {
+	config, err := LoadConfig()
+	if err != nil {
+		// If we can't load, create new config
+		config = &Config{Profiles: make(map[string]Profile)}
+	}
+
+	c.syncClientToConfig(config)
+
+	if err := SaveConfig(config); err != nil {
+		fmt.Println(yellow("Warning: Failed to save profiles:"), err)
+		return err
+	}
+
+	return nil
+}