feat: contact form backend for linux and freebsd servers

Assisted-by: GLM 5.3 Flash

man/nuntius.1

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+.TH NUNTIUS 1 2026-09-28 "nuntius 1.0.0" "nuntius manual"
+.SH NAME
+nuntius \- contact form backend
+.SH SYNOPSIS
+.B nuntius
+.RB [ \-\-version ]
+.RB [ \-\-check\-config ]
+.SH DESCRIPTION
+.B nuntius
+serves multiple JSON form endpoints (contact, feedback, newsletter,
+generic) from a single static binary, validates each submission, delivers
+it by SMTP and keeps per-form rate limits, CORS allowlists and a honeypot
+field. Newsletter forms use a double opt-in: the address is recorded only
+after the subscriber redeems the confirmation link from the mail.
+.PP
+Configuration is read from a TOML file, /etc/nuntius/config.toml by
+default. The first start writes a three-form starter template when the
+file does not exist, and every ${VAR} reference inside it is expanded
+from the environment before parsing, so secrets stay out of the file.
+With no flags the server listens on the configured address and serves
+until SIGINT or SIGTERM, then drains in-flight requests and exits.
+.SH OPTIONS
+.TP
+.B \-\-version
+Print the release the binary was built at, then exit. A build at a tag
+reports the tag, a build from a commit reports a pseudo-version naming
+that commit, and a build outside version control reports (devel); a dirty
+tree appends +dirty.
+.TP
+.B \-\-check\-config
+Load and validate the configuration file, then exit without listening.
+Exits nonzero and names the problem on any error, so it can run as a
+systemd ExecStartPre.
+.SH EXIT STATUS
+.TP
+.B 0
+The requested operation succeeded: the version was printed, the
+configuration is valid, or the server shut down cleanly.
+.TP
+.B 1
+The configuration is missing, invalid or fails validation, or the server
+failed to serve.
+.SH CONFIGURATION
+The full schema, every key with its type, default and effect, is in
+.I docs/CONFIGURATION.md
+in the repository. Configuration is one TOML file holding a
+.B [server]
+table, a
+.B data_dir
+and one or more
+.B [[forms]]
+entries, each with its own SMTP settings, rate limit, CORS allowlist and
+honeypot field.
+.SH ENVIRONMENT
+.TP
+.B NUNTIUS_CONFIG
+Path of the configuration file to read instead of
+/etc/nuntius/config.toml.
+.SH FILES
+.TP
+.I /etc/nuntius/config.toml
+The default configuration file; written as a starter template on first
+start when missing.
+.TP
+.I data_dir/newsletter-<name>.jsonl
+The append-only newsletter subscriber log, where data_dir is the
+configured data directory (./data by default).
+.SH EXAMPLES
+Print the release:
+.PP
+.RS
+.nf
+nuntius \-\-version
+.fi
+.RE
+.PP
+Validate a configuration without listening:
+.PP
+.RS
+.nf
+NUNTIUS_CONFIG=./config.toml nuntius \-\-check\-config
+.fi
+.RE
+.SH AUTHOR
+Petr Balvín <opensource@petrbalvin.org> (https://petrbalvin.org)
+.SH LICENCE
+MIT License
+.SH SEE ALSO
+.IR docs/CONFIGURATION.md ,
+.IR docs/API.md ,
+.IR docs/DEPLOYMENT.md