Extract config structs into pkg/probodconfig

probod-bootstrap only needs the config struct definitions for
YAML marshaling but transitively pulled in ~40 heavy runtime
dependencies via pkg/probod. Move all config types and their
methods to a new pkg/probodconfig package and re-export them
from pkg/probod via type aliases for backward compatibility.

Signed-off-by: Émile Ré <emile@getprobo.com>

pkg/probodconfig/mailer_config.go

@@ -0,0 +1,29 @@
+// Copyright (c) 2026 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package probodconfig
+
+type MailerConfig struct {
+	MailerInterval int        `json:"mailer-interval"`
+	SenderName     string     `json:"sender-name"`
+	SenderEmail    string     `json:"sender-email"`
+	SMTP           SMTPConfig `json:"smtp"`
+}
+
+type SMTPConfig struct {
+	Addr        string `json:"addr"`
+	User        string `json:"user"`
+	Password    string `json:"password"`
+	TLSRequired bool   `json:"tls-required"`
+}