ci: run Renovate from asxpi/renovate

Renovate now runs from its own repository for every repo, with the
shared rules in its preset. Extend that preset here and keep only what
is specific to this repo (the Ansible var manager, the Paper JRE, the
runner and nix notes); drop the workflow that ran it for iac alone.

Assisted-by: Claude:opus-5-5

nixos/modules/restic-alert.py

@@ -0,0 +1,20 @@
+# Mail the tail of a failed unit's journal.
+# Usage: restic-alert <unit> <env file>
+import os, smtplib, socket, subprocess, sys
+from email.message import EmailMessage
+
+unit = sys.argv[1]
+env = dict(l.rstrip("\n").split("=", 1) for l in open(sys.argv[2]) if "=" in l)
+log = subprocess.run(["journalctl", "-u", unit, "-n", "60", "--no-pager", "-o", "cat"],
+                     capture_output=True, text=True).stdout
+
+msg = EmailMessage()
+msg["Subject"] = f"[{socket.gethostname()}] {unit} failed"
+msg["From"] = env["ALERT_SMTP_USER"]
+msg["To"] = env["ALERT_RECIPIENT"]
+msg.set_content(log)
+
+with smtplib.SMTP(env["ALERT_SMTP_HOST"], int(env["ALERT_SMTP_PORT"]), timeout=30) as s:
+    s.starttls()
+    s.login(env["ALERT_SMTP_USER"], env["ALERT_SMTP_PASSWORD"])
+    s.send_message(msg)