feat(gateway): Discord channel auto-creation on project bootstrap

When a project is bootstrapped, the gateway now calls onProjectCreated on all loaded plugins. The Discord plugin creates a text channel in the configured guild (mosaic-{slug}) and the channel ID is stored in the project metadata jsonb. Gracefully skips if Discord is not configured or guild is unavailable.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

plugins/discord/src/index.ts

@@ -1,4 +1,4 @@
-import { Client, GatewayIntentBits, type Message as DiscordMessage } from 'discord.js';
+import { ChannelType, Client, GatewayIntentBits, type Message as DiscordMessage } from 'discord.js';
 import { io, type Socket } from 'socket.io-client';
 
 export interface DiscordPluginConfig {
@@ -86,6 +86,34 @@ export class DiscordPlugin {
     await this.client.destroy();
   }
 
+  async createProjectChannel(project: {
+    id: string;
+    name: string;
+    description?: string;
+  }): Promise<{ channelId: string } | null> {
+    if (!this.config.guildId) return null;
+
+    const guild = this.client.guilds.cache.get(this.config.guildId);
+    if (!guild) return null;
+
+    // Slugify project name for channel: lowercase, replace spaces/special chars with hyphens
+    const channelName = `mosaic-${project.name
+      .toLowerCase()
+      .replace(/[^a-z0-9]+/g, '-')
+      .replace(/^-|-$/g, '')}`;
+
+    const channel = await guild.channels.create({
+      name: channelName,
+      type: ChannelType.GuildText,
+      topic: project.description ?? `Mosaic project: ${project.name}`,
+    });
+
+    // Register the channel mapping so messages route correctly
+    this.channelConversations.set(channel.id, `discord-${channel.id}`);
+
+    return { channelId: channel.id };
+  }
+
   private handleDiscordMessage(message: DiscordMessage): void {
     // Ignore bot messages
     if (message.author.bot) return;