feat: add DBOS skills for TypeScript, Python, and Go (#94)

Add three DBOS SDK skills with reference documentation for building
reliable, fault-tolerant applications with durable workflows.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

skills/dbos-python/references/comm-messages.md

@@ -0,0 +1,56 @@
+---
+title: Use Messages for Workflow Notifications
+impact: MEDIUM
+impactDescription: Enables external signals to control workflow execution
+tags: messages, send, recv, notifications
+---
+
+## Use Messages for Workflow Notifications
+
+Send messages to workflows to signal or notify them while running. Messages are persisted and queued per topic.
+
+**Incorrect (polling external state):**
+
+```python
+@DBOS.workflow()
+def payment_workflow():
+    # Polling is inefficient and not durable
+    while True:
+        status = check_payment_status()
+        if status == "paid":
+            break
+        time.sleep(1)
+```
+
+**Correct (using messages):**
+
+```python
+PAYMENT_STATUS = "payment_status"
+
+@DBOS.workflow()
+def payment_workflow():
+    # Process order...
+    DBOS.set_event("payment_id", payment_id)
+
+    # Wait for payment notification (60 second timeout)
+    payment_status = DBOS.recv(PAYMENT_STATUS, timeout_seconds=60)
+
+    if payment_status == "paid":
+        fulfill_order()
+    else:
+        cancel_order()
+
+# Webhook endpoint to receive payment notification
+@app.post("/payment_webhook/{workflow_id}/{status}")
+def payment_webhook(workflow_id: str, status: str):
+    DBOS.send(workflow_id, status, PAYMENT_STATUS)
+    return {"ok": True}
+```
+
+Key points:
+- `DBOS.recv()` can only be called from workflows
+- Messages are queued per topic
+- `recv()` returns `None` on timeout
+- Messages are persisted for exactly-once delivery
+
+Reference: [Workflow Messaging](https://docs.dbos.dev/python/tutorials/workflow-communication#workflow-messaging-and-notifications)