feat: add Sardis payment tools for ADK agents

tools/sardis/README.md

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+# Sardis Payment Tools for Google ADK
+
+Policy-controlled payments for AI agents built with [Google Agent Development Kit](https://google.github.io/adk-docs/).
+
+## Installation
+
+```bash
+pip install sardis-adk
+```
+
+## Setup
+
+Set your environment variables:
+
+```bash
+export SARDIS_API_KEY="sk_..."
+export SARDIS_WALLET_ID="wal_..."
+```
+
+## Usage
+
+```python
+from google.adk.agents import Agent
+from tools.sardis import sardis_pay, sardis_check_balance, sardis_check_policy
+
+agent = Agent(
+    model="gemini-2.0-flash",
+    name="payment_agent",
+    description="An agent that can make policy-controlled payments",
+    tools=[sardis_pay, sardis_check_balance, sardis_check_policy],
+)
+```
+
+## Available Tools
+
+| Tool | Description |
+|------|-------------|
+| `sardis_pay` | Execute a payment with policy guardrails |
+| `sardis_check_balance` | Check wallet balance and spending limits |
+| `sardis_check_policy` | Pre-check if a payment would be allowed |
+
+## Features
+
+- **Policy guardrails** — spending limits, merchant restrictions, category rules
+- **Non-custodial** — MPC wallets, no private keys stored
+- **Multi-chain** — Base, Polygon, Ethereum, Arbitrum, Optimism
+- **Stablecoin native** — USDC, USDT, EURC, PYUSD
+- **Full audit trail** — append-only ledger for compliance
+
+## Links
+
+- [Sardis Documentation](https://sardis.sh/docs)
+- [sardis-adk on PyPI](https://pypi.org/project/sardis-adk/)
+- [GitHub](https://github.com/EfeDurmaz16/sardis)

tools/sardis/__init__.py

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+"""Sardis payment tools for Google ADK agents."""
+
+from sardis_adk.tools import (
+    sardis_pay,
+    sardis_check_balance,
+    sardis_check_policy,
+    SARDIS_TOOLS,
+)
+
+__all__ = [
+    "sardis_pay",
+    "sardis_check_balance",
+    "sardis_check_policy",
+    "SARDIS_TOOLS",
+]

tools/sardis/sardis_tool.py

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+"""Sardis payment tool for Google Agent Development Kit.
+
+This tool enables ADK agents to make policy-controlled payments through
+Sardis non-custodial MPC wallets.
+
+Installation:
+    pip install sardis-adk
+
+Usage:
+    from tools.sardis import sardis_pay, sardis_check_balance
+
+    # Use in an ADK agent
+    agent = Agent(
+        model="gemini-2.0-flash",
+        name="payment_agent",
+        tools=[sardis_pay, sardis_check_balance],
+    )
+"""
+
+from sardis_adk.tools import (
+    sardis_pay,
+    sardis_check_balance,
+    sardis_check_policy,
+    SARDIS_TOOLS,
+)
+
+__all__ = [
+    "sardis_pay",
+    "sardis_check_balance",
+    "sardis_check_policy",
+    "SARDIS_TOOLS",
+]