feat: add support for Anthropic and DeepSeek AI providers

[shenxianpeng]

Testing done

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed

[Copilot]

Pull request overview

Adds two new AI providers (Anthropic Claude and DeepSeek) to the Explain Error Jenkins plugin, including Jenkins UI configuration, CasC examples/tests, and provider validation coverage.

Changes:

• Introduce AnthropicProvider and DeepSeekProvider implementations (LangChain4j-backed) with corresponding config.jelly UI.
• Add Configuration-as-Code (CasC) YAML fixtures + JCasC tests for the new providers.
• Update dependency set (LangChain4j Anthropic module) and extend README provider documentation.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/main/java/io/jenkins/plugins/explain_error/provider/AnthropicProvider.java	New Anthropic provider implementation + descriptor/UI endpoints
src/main/java/io/jenkins/plugins/explain_error/provider/DeepSeekProvider.java	New DeepSeek provider implementation + descriptor/UI endpoints
src/main/resources/io/jenkins/plugins/explain_error/provider/AnthropicProvider/config.jelly	UI form for Anthropic configuration
src/main/resources/io/jenkins/plugins/explain_error/provider/DeepSeekProvider/config.jelly	UI form for DeepSeek configuration
src/test/java/io/jenkins/plugins/explain_error/CasCTest.java	Adds JCasC tests for Anthropic/DeepSeek
src/test/java/io/jenkins/plugins/explain_error/provider/ProviderTest.java	Adds config-validation tests for Anthropic/DeepSeek
src/test/java/io/jenkins/plugins/explain_error/provider/TestAnthropicProvider.java	Test provider stub for Anthropic
src/test/java/io/jenkins/plugins/explain_error/provider/TestDeepSeekProvider.java	Test provider stub for DeepSeek
src/test/resources/io/jenkins/plugins/explain_error/casc_anthropic.yaml	CasC fixture for Anthropic
src/test/resources/io/jenkins/plugins/explain_error/casc_deepseek.yaml	CasC fixture for DeepSeek
pom.xml	Adds langchain4j-anthropic dependency
README.md	Documents Anthropic/DeepSeek configuration and provider notes
.github/copilot-instructions.md	Updates architecture/provider list to include new providers