docs: Add Spraay batch payment tools to third-party catalog

[plagtech]

What

Adds Spraay to the Third-Party Tools catalog — a multi-chain batch payment protocol that enables ADK agents to send ETH or ERC-20 tokens to 200+ recipients in a single transaction.

Why

Batch payments (payroll, airdrops, bounties, reward distributions) are a common need for AI agents operating onchain. Spraay provides both an MCP server integration and native ADK community tools, making it easy for any ADK agent to execute batch payments on Base with ~80% gas savings.

What's Added

• docs/tools/third-party/spraay/index.md — Integration documentation with MCP and community tool usage examples
• docs/assets/tools-spraay.png — Spraay logo for the tools grid
• Entry added to docs/tools/third-party/index.md grid
• Navigation entry added to mkdocs.yml

Integration Methods

1. MCP Server (spraay-x402-mcp) — 9 paid endpoints via x402 protocol, no API keys needed. Listed on Smithery, MCP.so, LobeHub, and the x402 ecosystem.
2. Community Tools — Native ADK function tools submitted to google/adk-python-community (PR #95).

Checklist

• Documentation follows existing third-party tool format
• Logo matches dimensions of existing tool logos
• MCP integration example included
• Community tool integration example included
• All external links verified

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[koverholt]

Thank you for the PR. After reviewing this PR against our acceptance criteria, we're not able to accept this integration at this time.

Completeness and testability: While the MCP tool example would be functional, the community tools example imports from google.adk_community.tools.spraay and the corresponding PR has not been reviewed or merged. Code examples in our docs must be functional and runnable by developers. Additionally, this PR is using a deprecated format for integration pages.

Value for developers: We look for integrations that provide clear, demonstrated value to developers building agents with ADK. We evaluate factors such as project maturity, active user base, and track record when assessing whether an integration is appropriate for inclusion in our official documentation. This project is very new as of a few days ago and does not yet have community adoption or a track record that would help us assess that value for our users.