feat(server): use configurable startup settings

Load the listen address and port from settings, print connection guidance and explain startup failures.

server.py

@@ -4,8 +4,10 @@ from __future__ import annotations
 import os
 import sys
 import time
+import socket
+
+from server_config import load_config
 
-PORT = int(os.environ.get("REXIMEMO_PORT", "8080"))
 DOCS_ARGUMENT = "docs:enabled"
 
 
@@ -68,13 +70,41 @@ def create_site(*, docs_enabled=False):
 
 
 def main():
+    settings = load_config()
+    try:
+        port = int(os.environ.get("REXIMEMO_PORT", settings["port"]))
+        if not 1024 <= port <= 65535:
+            raise ValueError
+    except ValueError as exc:
+        raise SystemExit("Choose a port between 1024 and 65535 in server-settings.json or REXIMEMO_PORT.") from exc
+    host = os.environ.get("REXIMEMO_HOST", settings["host"])
     docs_enabled = docs_enabled_from_args()
     reactor, site, log = create_site(docs_enabled=docs_enabled)
-    log.write("RexiMemo OSE starting on port %d" % PORT)
+    log.write("%s starting on %s:%d" % (settings["site_name"], host, port))
+    log.write("Web client: http://127.0.0.1:%d/" % port)
+    try:
+        addresses = sorted({address[4][0] for address in socket.getaddrinfo(socket.gethostname(), None, socket.AF_INET)
+                            if not address[4][0].startswith("127.")})
+    except OSError:
+        addresses = []
+    if host in {"0.0.0.0", "::"}:
+        for address in addresses:
+            log.write("DSi HTTP proxy: %s, port %d" % (address, port))
+    elif host not in {"127.0.0.1", "::1", "localhost"}:
+        log.write("DSi HTTP proxy: %s, port %d" % (host, port))
+    else:
+        log.write("Listening on this computer only. For a DSi on your network, choose listen address 0.0.0.0 during setup.")
+    if not settings["setup_complete"]:
+        log.write("First-run setup is available: python manage.py setup")
     log.write("DSi mode uses the historical HTTP proxy path; NAS/DNS/auth services are not included.")
     if docs_enabled:
         log.write("Built-in documentation enabled at /docs")
-    reactor.listenTCP(PORT, site)
+    from twisted.internet.error import CannotListenError
+    try:
+        reactor.listenTCP(port, site, interface=host)
+    except CannotListenError as exc:
+        log.close()
+        raise SystemExit(f"Could not listen on {host}:{port}. Another server may already use that port. Stop it or choose another port with: python manage.py setup") from exc
     try:
         reactor.run()
     finally: