Add Maestro-style YAML flow runner for deterministic automation

New --flow mode executes scripted YAML steps without LLM, mapping 17
commands (tap, type, swipe, scroll, etc.) to existing actions. Element
finding uses accessibility tree text/hint/id matching.

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

examples/flows/send-whatsapp.yaml

@@ -0,0 +1,14 @@
+appId: com.whatsapp
+name: Send WhatsApp Message
+---
+- home
+- wait: 1
+- launchApp
+- wait: 2
+- tap: "Vi"
+- wait: 1
+- tap: "Message"
+- type: "hello from Droidclaw"
+- tap: "Send"
+- wait: 1
+- done: "Message sent"