Add AgentMail: paid-member mailbox reader (TUI + bot mode) on the BBS

internal/mailbox is a transport-agnostic mail client for Founding Lifetime
members: read, search, compose, send, reply, flag, delete.

- types/transport/client: paid-gated facade returning JSON-serializable
  structs (same shapes as @logicsrc/plugin-agentmail)
- memory.go: in-memory transport (tests/dev/reference) + tests
- imap.go/smtp.go: real backend — go-imap/v2 (Dovecot IMAP, master-user
  login) + net/smtp submission via the co-located relay; go-message parses
  bodies/attachments
- reader_tui.go: Bubble Tea reader for humans (list/read/flag/delete)
- bot.go: JSON in/out mode for agents (ssh mail@host list|read|send|…)
- wired as the paid "Mail" hub entry and the ssh mail@ route + auth.MailNames

Connects to the self-hosted Mailu stack at mail.profullstack.com /
smtp.profullstack.com. Rebased onto main; build + vet + tests clean (Go 1.26).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

go.mod

@@ -10,6 +10,8 @@ require (
 	github.com/charmbracelet/wish v1.4.7
 	github.com/creack/pty v1.1.24
 	github.com/dustin/go-nntp v0.0.0-20210723005859-f00d51cf8cc1
+	github.com/emersion/go-imap/v2 v2.0.0-beta.8
+	github.com/emersion/go-message v0.18.2
 	github.com/gorilla/websocket v1.5.4-0.20250319132907-e064f32e3674
 	github.com/livekit/protocol v1.46.0
 	github.com/livekit/server-sdk-go/v2 v2.16.6
@@ -46,6 +48,7 @@ require (
 	github.com/dennwc/iters v1.2.2 // indirect
 	github.com/dgryski/go-rendezvous v0.0.0-20200823014737-9f7001d12a5f // indirect
 	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/emersion/go-sasl v0.0.0-20241020182733-b788ff22d5a6 // indirect
 	github.com/erikgeiser/coninput v0.0.0-20211004153227-1c3628e74d0f // indirect
 	github.com/frostbyte73/core v0.1.1 // indirect
 	github.com/fsnotify/fsnotify v1.9.0 // indirect