feat: implement Go-based mail2couch with working IMAP and CouchDB integration

- Add configuration system with automatic file discovery (current dir, config subdir, user home, XDG config)
- Implement IMAP client with TLS connection, authentication, and mailbox listing
- Add CouchDB integration with database creation and document storage
- Support folder filtering (include/exclude) and date filtering (since parameter)
- Include duplicate detection to prevent re-storing existing messages
- Add comprehensive error handling and logging throughout
- Structure code in clean packages: config, mail, couch
- Application currently uses placeholder messages to test the storage pipeline
- Ready for real IMAP message parsing implementation

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

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

go/config/config.go

@@ -0,0 +1,111 @@
+package config
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+type Config struct {
+	CouchDb     CouchDbConfig `json:"couchDb"`
+	MailSources []MailSource  `json:"mailSources"`
+}
+
+type CouchDbConfig struct {
+	URL      string `json:"url"`
+	User     string `json:"user"`
+	Password string `json:"password"`
+	Database string `json:"database"`
+}
+
+type MailSource struct {
+	Name          string        `json:"name"`
+	Enabled       bool          `json:"enabled"`
+	Protocol      string        `json:"protocol"`
+	Host          string        `json:"host"`
+	Port          int           `json:"port"`
+	User          string        `json:"user"`
+	Password      string        `json:"password"`
+	Sync          bool          `json:"sync"`
+	FolderFilter  FolderFilter  `json:"folderFilter"`
+	MessageFilter MessageFilter `json:"messageFilter"`
+}
+
+type FolderFilter struct {
+	Include []string `json:"include"`
+	Exclude []string `json:"exclude"`
+}
+
+type MessageFilter struct {
+	Since string `json:"since,omitempty"`
+}
+
+func LoadConfig(path string) (*Config, error) {
+	configFile, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer configFile.Close()
+
+	var config Config
+	jsonParser := json.NewDecoder(configFile)
+	if err = jsonParser.Decode(&config); err != nil {
+		return nil, err
+	}
+
+	return &config, nil
+}
+
+// FindConfigFile searches for config.json in the following order:
+// 1. Path specified by -config flag
+// 2. ./config.json (current directory)
+// 3. ~/.config/mail2couch/config.json (user config directory)
+// 4. ~/.mail2couch.json (user home directory)
+func FindConfigFile() (string, error) {
+	// Check for command line flag
+	configFlag := flag.String("config", "", "Path to configuration file")
+	flag.Parse()
+
+	if *configFlag != "" {
+		if _, err := os.Stat(*configFlag); err == nil {
+			return *configFlag, nil
+		}
+		return "", fmt.Errorf("specified config file not found: %s", *configFlag)
+	}
+
+	// List of possible config file locations in order of preference
+	candidates := []string{
+		"config.json",        // Current directory
+		"config/config.json", // Config subdirectory
+	}
+
+	// Add user directory paths
+	if homeDir, err := os.UserHomeDir(); err == nil {
+		candidates = append(candidates,
+			filepath.Join(homeDir, ".config", "mail2couch", "config.json"),
+			filepath.Join(homeDir, ".mail2couch.json"),
+		)
+	}
+
+	// Try each candidate location
+	for _, candidate := range candidates {
+		if _, err := os.Stat(candidate); err == nil {
+			return candidate, nil
+		}
+	}
+
+	return "", fmt.Errorf("no configuration file found. Searched locations: %v", candidates)
+}
+
+// LoadConfigWithDiscovery loads configuration using automatic file discovery
+func LoadConfigWithDiscovery() (*Config, error) {
+	configPath, err := FindConfigFile()
+	if err != nil {
+		return nil, err
+	}
+
+	fmt.Printf("Using configuration file: %s\n", configPath)
+	return LoadConfig(configPath)
+}