feat(channels): add mattermost adapter and wiring

src/gateway/handlers/config.ts

@@ -11,7 +11,7 @@ export interface ConfigHandlerDeps {
  * Redact sensitive values from config before returning.
  * Replaces API keys, tokens, passwords, and other credentials with "***".
  *
- * Covers: telegram, discord, slack, matrix, server, models (tiers + fallbacks + local_providers),
+ * Covers: telegram, discord, slack, matrix, mattermost, server, models (tiers + fallbacks + local_providers),
  * web_search, audio, memory.embedding, automation (webhooks + gmail), and mcp server env vars.
  */
 export function redactConfig(config: Config): Record<string, unknown> {
@@ -37,6 +37,9 @@ export function redactConfig(config: Config): Record<string, unknown> {
   // Matrix
   redact(raw.matrix as Record<string, unknown>, 'access_token');
 
+  // Mattermost
+  redact(raw.mattermost as Record<string, unknown>, 'bot_token');
+
   // Server (gateway bearer token)
   redact(raw.server as Record<string, unknown>, 'token');