gdo: the code that opens the iris

A durable consumer on portal's WORMHOLE stream, each message handed to
the host's SMTP as text with an HTML alternative; acked on acceptance,
retried after a minute otherwise, left for a newer gdo when the
contract version is unknown. `gdo probe <to>` sends one through and
waits for the consumer to drain. GDO_TYPST_THEME attaches a Typst PDF.
A systemd unit and an installer for one gdo per host.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01L4jrCgLiKKHAEFuZUJjckH

Cargo.toml

@@ -0,0 +1,22 @@
+[package]
+name = "gdo"
+version = "0.1.0"
+edition = "2021"
+description = "Sends the code that opens the iris: delivers portal's outgoing mail from JetStream to the host's SMTP"
+license = "MIT"
+repository = "https://project.uhhm.no/uhhm/gdo"
+
+[dependencies]
+anyhow = "1"
+async-nats = "0.38"
+futures = "0.3"
+lettre = { version = "0.11", default-features = false, features = ["builder", "smtp-transport", "tokio1", "hostname"] }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+tokio = { version = "1", features = ["rt-multi-thread", "macros", "signal", "process", "fs"] }
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }
+
+[profile.release]
+strip = true
+lto = "thin"