[AAASM-2308] ✨ (scenarios): Add approval-gates/ scaffold and Python implementation

[Chisanan232]

What changed

Adds the scenarios/approval-gates/ directory with shared scenario files and a fully-offline Python sub-project demonstrating the pending → approved → executed approval flow.

Shared scenario files:

• scenarios/approval-gates/policy.yaml — 2-rule policy: get_balance (allow), transfer_funds (approval_required), default_action: deny
• scenarios/approval-gates/expected-output.txt — terminal output reference showing the pending → approved → executed cycle
• scenarios/approval-gates/README.md — concept explanation, approval flow walkthrough, run instructions, real-app guidance

Python sub-project (scenarios/approval-gates/python/):

• ApprovalPolicyEngine handles allow, deny, and approval_required actions from policy.yaml
• MockApprovalClient simulates a real approval service: auto-approves or rejects, prints pending/approved messages
• governed() wrapper is approval-aware — tool body only runs after approval is granted
• 8 smoke tests: allowed tool, approved transfer, rejected transfer, body-never-executes, default deny, mock client behavior

Related ticket

Closes AAASM-2308

How to verify

cd scenarios/approval-gates/python
uv sync --extra dev
uv run python src/main.py    # shows pending → approved → executed
uv run pytest tests/ -v      # 8 tests pass

Checklist

• PR title follows [AAASM-XXXX] <GitEmoji> (<scope>): <summary>
• No secrets, API keys, or .env files committed
• Example sub-projects include their own README.md via the scenario-level README
• SDK/runtime version dependencies are documented or pinned

[sonarqubecloud]

Quality Gate passed

Issues
4 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud