contributing/samples: add Synap memory agent sample

[visy-ani]

Summary

Adds contributing/samples/synap_memory_agent/ — a sample showing how to give an ADK Agent persistent, cross-session memory via Synap.

The agent is wired with two FunctionTool instances built from synap-google-adk:

• search_memory — semantic search over the user's stored memories
• store_memory — persist explicit facts the user mentions

PyPI: https://pypi.org/project/synap-google-adk/
Open source: https://github.com/maximem-ai/maximem_synap_sdk/tree/main/packages/integrations/synap-google-adk

Test plan

• adk run contributing/samples/synap_memory_agent runs end-to-end with SYNAP_API_KEY set

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[visy-ani]

@googlebot I signed it!

Hi @wyf7107 and @ankursharmas 👋 — would love a review on this whenever you have a moment! This adds contributing/samples/synap_memory_agent/ — an ADK Agent sample showing how to plug long-term, cross-session memory into ADK via Synap.

Why this fits contributing/samples/: it follows the same shape as the other samples in that folder (single agent.py with root_agent, __init__.py, and a README) and only adds two FunctionTool instances from synap-google-adk — no new core ADK dependencies. The sample is runnable with adk run contributing/samples/synap_memory_agent.

CLA has now been signed (just commented above to trigger re-check). Header-check is already green. Thanks!