build: resolve --remote as SSH config alias when it has no @

scripts/build-and-push.sh now parses ~/.ssh/config (or --ssh-config)
when --remote is a bare alias like 'prod'. It extracts HostName,
User, Port and IdentityFile from the matching Host block, falls back
to the current user / port 22, and uses the config IdentityFile when
--ssh-key is not given. --ssh-key always wins. The resolved target
is shown in the logs before any docker/pussh call, and is the form
passed to docker pussh and the verification ssh.

Wildcards, Include and Match directives are intentionally not handled:
ssh itself resolves them when the alias is passed through, but the
script logs the expanded target first for visibility.

README.md

@@ -22,6 +22,29 @@ It can be invoked from any directory: by default it resolves the project root
 from the script's own location. Override with `--project-dir PATH` or the
 `PROJECT_DIR` environment variable when needed.
 
+### SSH config aliases
+
+`--remote` accepts either an explicit `user@host[:port]` or a bare alias that
+is resolved from `~/.ssh/config`. The matching `Host` block supplies
+`HostName`, `User`, `Port` and `IdentityFile` automatically:
+
+```text
+# ~/.ssh/config
+Host prod
+    HostName prod.example.com
+    User deploy
+    Port 22
+    IdentityFile ~/.ssh/deploy_ed25519
+```
+
+```shell script
+./scripts/build-and-push.sh --remote prod
+# Resolves to deploy@prod.example.com:22 using ~/.ssh/deploy_ed25519
+```
+
+`--ssh-key` always overrides the config `IdentityFile`. Use `--ssh-config PATH`
+to point at a non-default config file.
+
 ## Running the application in dev mode
 
 You can run your application in dev mode that enables live coding using: