docs(uipath-maestro-flow): add fast-path flow example

[kab0rn]

Summary

• Add a validator-clean decision-branch.flow example for the common manual trigger -> script -> decision -> branch scripts -> End-node pattern.
• Document the example as the fast path for common branching flows and clarify when agents should avoid inline node add --input shell-escaping loops.
• Add helper pytest coverage for the example topology, outputs, definitions, and horizontal layout.

Why

Agents building Flow projects can lose time fighting inline JSON quoting for $vars, template literals, and multiline scripts. A complete .flow baseline gives them a copyable, validated starting point for a common branching pattern while preserving the Direct JSON default.

Refs #114

Validation

• git diff --check
• bash hooks/validate-skill-descriptions.sh skills/uipath-maestro-flow/SKILL.md
• python3 -m pytest tests/tasks/uipath-maestro-flow/_shared -q
• npx -y @uipath/cli@latest maestro flow validate skills/uipath-maestro-flow/references/examples/decision-branch.flow --output json