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/go.mod

@@ -0,0 +1,16 @@
+module mail2couch
+
+go 1.24.4
+
+require (
+	github.com/emersion/go-imap/v2 v2.0.0-beta.5
+	github.com/go-kivik/kivik/v4 v4.4.0
+)
+
+require (
+	github.com/emersion/go-message v0.18.1 // indirect
+	github.com/emersion/go-sasl v0.0.0-20231106173351-e73c9f7bad43 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	golang.org/x/net v0.25.0 // indirect
+	golang.org/x/sync v0.10.0 // indirect
+)