feat(samples): add sample for skill activation via environment tools

[Jacksunwei]

Link to Issue or Description of Change

1. Link to an existing issue (if applicable):
(None, this is a new sample)

2. Or, if no issue exists, describe the change:

Problem:
There was no sample demonstrating how to use LocalEnvironment with EnvironmentToolset for manual skill activation (discovering and loading skills by reading files) instead of using the pre-configured SkillToolset.

Solution:
Created a new sample local_environment_skill that demonstrates this pattern:

• Agent is instructed to find skills in skills/ folder using the find command.
• Agent loads skills by reading SKILL.md using the ReadFile tool.
• Added a weather skill sample and reference data to demonstrate usage.

Testing Plan

Unit Tests:
(This is a sample/demonstration, so no new unit tests were added for the framework itself.)

Manual End-to-End (E2E) Tests:

1. Ran adk web contributing/samples.
2. Interacted with the agent in the Web UI.
3. Prompt: "Can you check the weather in Sunnyvale?"
4. Verified that the agent successfully used find to locate the skill, read SKILL.md, read weather_info.md, and answered correctly.

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have manually tested my changes end-to-end.

[adk-bot]

Response from ADK Triaging Agent

Hello @Jacksunwei, thank you for creating this PR!

It seems like the pyink-check is failing. Could you please run ./autoformat.sh to fix the code formatting?

This will help to get your PR merged faster. Thanks!