feat: Discord + Instagram integrations

Discord Bot API
- New client: src/clients/discord.ts
- Tools: discord_get_me, discord_get_guilds, discord_get_channels, discord_send_message, discord_get_messages
- REST endpoints: GET /api/discord/me, /api/discord/guilds, /api/discord/channels, /api/discord/messages, POST /api/discord/message
- Multi-account env var: DISCORD_{ACCOUNT}_BOT_TOKEN

Instagram Graph API
- New client: src/clients/instagram.ts
- Tools: instagram_get_profile, instagram_get_media, instagram_create_post
- REST endpoints: GET /api/instagram/profile, /api/instagram/media, POST /api/instagram/post
- Multi-account env vars: INSTAGRAM_{ACCOUNT}_ACCESS_TOKEN, INSTAGRAM_{ACCOUNT}_BUSINESS_ACCOUNT_ID

Total tools: 32

.env.example

@@ -60,3 +60,17 @@ LINKEDIN_DEFAULT_CLIENT_SECRET=your-linkedin-client-secret
 # For default account:
 TELEGRAM_DEFAULT_BOT_TOKEN=your-telegram-bot-token
 # For additional accounts, duplicate with TELEGRAM_{ACCOUNT}_*
+
+# ── Discord Bot API ──────────────────────────────────────────────────────────
+# Create a bot at https://discord.com/developers/applications → New Application → Bot → Copy Token
+# For default account:
+DISCORD_DEFAULT_BOT_TOKEN=your-discord-bot-token
+# For additional accounts, duplicate with DISCORD_{ACCOUNT}_*
+
+# ── Instagram Graph API ──────────────────────────────────────────────────────
+# Requires Instagram Business/Creator account connected to Facebook Page
+# Get token from Facebook Developer Console with instagram_basic + instagram_content_publish scopes
+# For default account:
+INSTAGRAM_DEFAULT_ACCESS_TOKEN=your-instagram-access-token
+INSTAGRAM_DEFAULT_BUSINESS_ACCOUNT_ID=your-instagram-business-account-id
+# For additional accounts, duplicate with INSTAGRAM_{ACCOUNT}_*