feat(channels): add mattermost adapter and wiring

src/config/schema.ts

@@ -449,6 +449,15 @@ const signalSchema = z.object({
   send_timeout_ms: z.number().min(1000).max(60000).default(15000),
 }).optional();
 
+const mattermostSchema = z.object({
+  server_url: z.string().url('Mattermost server_url must be a valid URL'),
+  bot_token: z.string().min(1, 'Mattermost bot_token is required'),
+  allowed_channel_ids: z.array(z.string()).default([]),
+  require_mention: z.boolean().default(true),
+  mention_name: z.string().default('flynn'),
+  poll_interval_ms: z.number().min(1000).max(60000).default(3000),
+}).optional();
+
 const teamsSchema = z.object({
   app_id: z.string().min(1, 'Teams app_id is required'),
   app_password: z.string().min(1, 'Teams app_password is required'),
@@ -648,6 +657,7 @@ export const configSchema = z.object({
   whatsapp: whatsappSchema,
   matrix: matrixSchema,
   signal: signalSchema,
+  mattermost: mattermostSchema,
   teams: teamsSchema,
   google_chat: googleChatSchema,
   bluebubbles: bluebubblesSchema,
@@ -696,6 +706,7 @@ export type SlackConfig = z.infer<typeof slackSchema>;
 export type WhatsAppConfig = z.infer<typeof whatsappSchema>;
 export type MatrixConfig = z.infer<typeof matrixSchema>;
 export type SignalConfig = z.infer<typeof signalSchema>;
+export type MattermostConfig = z.infer<typeof mattermostSchema>;
 export type TeamsConfig = z.infer<typeof teamsSchema>;
 export type GoogleChatConfig = z.infer<typeof googleChatSchema>;
 export type BlueBubblesConfig = z.infer<typeof bluebubblesSchema>;