docs: split bot.toml.example into per-transport example files

Replace the monolithic bot.toml.example with separate files for each
transport: matrix, whatsapp-meta, whatsapp-twilio, and slack. Add a
chat bot configuration section to the README explaining that only one
transport can be active at a time and how to set up each one.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.storkit/bot.toml.whatsapp-meta.example

@@ -0,0 +1,28 @@
+# WhatsApp Transport (Meta Cloud API)
+# Copy this file to bot.toml and fill in your values.
+# Only one transport can be active at a time.
+#
+# Setup:
+#   1. Create a Meta Business App at developers.facebook.com
+#   2. Add the WhatsApp product
+#   3. Copy your Phone Number ID and generate a permanent access token
+#   4. Register your webhook URL: https://your-server/webhook/whatsapp
+#   5. Set the verify token below to match what you configure in Meta's dashboard
+
+enabled = true
+transport = "whatsapp"
+whatsapp_provider = "meta"
+
+whatsapp_phone_number_id = "123456789012345"
+whatsapp_access_token = "EAAx..."
+whatsapp_verify_token = "my-secret-verify-token"
+
+# Optional: name of the approved Meta message template used for notifications
+# sent outside the 24-hour messaging window (default: "pipeline_notification").
+# whatsapp_notification_template = "pipeline_notification"
+
+# Bot display name (used in formatted messages).
+# display_name = "Assistant"
+
+# Maximum conversation turns to remember per user (default: 20).
+# history_size = 20