feat: add Slack bot integration

src/channels/slack/manifest.mjs

@@ -0,0 +1,31 @@
+export const SLACK_APP_MANIFEST_YAML = `_metadata:
+  major_version: 1
+display_information:
+  name: DeepSeek Harness
+  description: Connect Slack conversations to a local DeepSeek Harness agent.
+  background_color: "#4A154B"
+features:
+  app_home:
+    home_tab_enabled: false
+    messages_tab_enabled: true
+    messages_tab_read_only_enabled: false
+  bot_user:
+    display_name: DeepSeek Harness
+    always_online: false
+oauth_config:
+  scopes:
+    bot:
+      - app_mentions:read
+      - chat:write
+      - im:history
+settings:
+  event_subscriptions:
+    bot_events:
+      - app_mention
+      - message.im
+  org_deploy_enabled: false
+  socket_mode_enabled: true
+  token_rotation_enabled: false
+`;
+
+export const SLACK_CREATE_APP_URL = 'https://api.slack.com/apps?new_app=1';