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

.gitea/workflows/test.yml

@@ -0,0 +1,24 @@
+name: Test
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  test:
+    runs-on: bare
+    env:
+      # Same shared toolchain and cache as uhhm/portal's workflows, with
+      # the writable cargo home uhhm/iris uses.
+      CARGO_HOME: /var/local/cargo-target/iris-cargo-home
+      RUSTC_WRAPPER: /usr/bin/sccache
+      RUSTUP_HOME: /var/local/rustup
+      PATH: /var/local/cargo/bin:/usr/local/sbin:/usr/local/bin:/usr/bin
+      SCCACHE_DIR: /var/local/sccache
+      SCCACHE_SERVER_PORT: "4228"
+      CARGO_TARGET_DIR: /var/local/cargo-target
+    steps:
+      - uses: actions/checkout@v4
+      - name: Test
+        run: cargo test