Feat/mail all members (#55)

* feat(mail): give every verified member a free @bbs.profullstack.com mailbox

Email was built but paid-only (Founding Lifetime gate) and never wired to a
running backend. Make it a free benefit of membership and split the address
domain from the mail-server host.

- internal/mailu: Mailu admin-API client; EnsureUser idempotently provisions a
  mailbox via the loopback admin REST API (token = mailu.env API_TOKEN).
- main.go: auto-provision <name>@<mailDomain> at join@ verification and on first
  Mail open; un-gate the Mail hub entry + mail@ (membership/email-verified, not
  Premium); address domain (AGENTBBS_MAIL_ADDR_DOMAIN, default the BBS host) is
  now distinct from the mail server host (AGENTBBS_MAIL_DOMAIN) and the webmail
  URL. Drop the forwardemail alias path (Mailu now owns delivery for everyone).
- mailbox: gate on membership (a registered handle) instead of Paid;
  ErrNotPaid -> ErrNotMember.
- join@ copy: list email under free membership; premium now pitches custom
  domains + Tor only.
- setup.sh / docs/mail.md / deploy/mailu: address-domain vs server-host split,
  Mailu API token, MX for the address domain, local-relay SMTP for verify codes.

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

* chore(mailu): pin Docker network subnet to match SUBNET; ignore runtime state

The base compose declares no network, so Docker assigns the default bridge an
arbitrary subnet that won't match mailu.env SUBNET — breaking Mailu's internal
service auth/relay. Add a docker-compose.override.yml.example that pins the
default network to 192.168.203.0/24, and gitignore the live override + Mailu
runtime state (mailu.env, certs/, data/).

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

* feat(mail): plaintext loopback IMAP so the gateway bypasses Mailu's front

Mailu's front (nginx mail proxy) pre-authenticates against Mailu's user DB before
proxying to Dovecot, which rejects the Dovecot master-user login <addr>*gateway.
The gateway must reach Dovecot directly. The imap container has no TLS cert (only
the front does), so the bypass is plaintext over loopback — the master password
never leaves the host.

- mailbox: IMAPConfig.Plaintext dials with DialInsecure (loopback only).
- main.go: mailClientFor sets Plaintext from AGENTBBS_MAIL_IMAP_PLAINTEXT.
- override.example: add the unbound resolver (admin needs DNSSEC), webmail image
  fix (2024.06 uses mailu/webmail), and publish Dovecot 143 on 127.0.0.1:14143.
- docs/mail.md: document the front-bypass, the dovecot.conf master passdb (Mailu
  includes that exact filename), and the 644 master-users perms (640 = temp_fail).

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

* deploy(mailu): wire gateway IMAP to the loopback Dovecot path in setup.sh

setup.sh §9e set AGENTBBS_MAIL_IMAP_ADDR to the front's :993, which the front's
auth proxy rejects for the master-user login (and would clobber the working
loopback wiring on every self-update). Point it at 127.0.0.1:14143 +
AGENTBBS_MAIL_IMAP_PLAINTEXT=1 instead, matching the override + docs.

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

* feat(mail): give free members a webmail password at join@

The gateway opens mailboxes via the Dovecot master user (no member password),
but webmail (Roundcube) needs the member to have a password. join@ now sets a
fresh, readable webmail password via the Mailu API and shows it with the webmail
URL + login, so free members can use webmail at mail.profullstack.com.

- mailu: SetPassword (PATCH /user/<email> raw_password) + test.
- main.go: setWebmailPassword + readablePassword; join@ displays url/login/password.

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

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

internal/mailbox/imap.go

@@ -24,6 +24,11 @@ type IMAPConfig struct {
 	// SMTPUser/SMTPPass default to Username/Password when empty.
 	SMTPUser string
 	SMTPPass string
+	// Plaintext dials IMAP without TLS. Used only for a co-located backend over
+	// loopback (the Mailu gateway hitting Dovecot directly on 127.0.0.1, bypassing
+	// the front's auth proxy so master-user login works) — the password never
+	// leaves the host. Never enable it for a remote server.
+	Plaintext bool
 }
 
 // imapTransport is a Transport backed by a single authenticated IMAP connection
@@ -38,7 +43,11 @@ type imapTransport struct {
 
 // NewIMAPTransport dials the IMAP server, logs in, and returns a Transport.
 func NewIMAPTransport(cfg IMAPConfig) (Transport, error) {
-	c, err := imapclient.DialTLS(cfg.IMAPAddr, nil)
+	dial := imapclient.DialTLS
+	if cfg.Plaintext {
+		dial = imapclient.DialInsecure
+	}
+	c, err := dial(cfg.IMAPAddr, nil)
 	if err != nil {
 		return nil, fmt.Errorf("imap dial %s: %w", cfg.IMAPAddr, err)
 	}