Migrate from deprecated gemini-1.5-flash and @google/generative-ai to current packages

[Copilot]

Migration from deprecated packages to current ones

This PR migrates from deprecated packages to their current replacements:

• gemini-1.5-flash → gemini-2.5-flash
• @google/generative-ai → @google/genai

Migration Plan

• Analyze current codebase and understand the deprecated API usage
• Research the new @google/genai package API structure
• Update package.json to replace @google/generative-ai with @google/genai
• Update the main gemini.ts file to use the new API:
  • Change import from @google/generative-ai to @google/genai
  • Replace GoogleGenerativeAI with GoogleGenAI
  • Update the API usage from genAI.getGenerativeModel() to ai.models.generateContent()
  • Update model name from gemini-1.5-flash to gemini-2.5-flash
  • Update proxy fallback to use httpOptions.baseUrl
• Update files consuming the gemini API:
  • Fix response handling in app/actions/chatActions.ts (from result.response.text() to result.text)
  • Fix response handling in app/actions/questionExample.ts (from result.response.text() to result.text)
  • Add proper null checks for the text response
• Extract model and contents parameters into reusable params variable for better maintainability
• Verify that all files importing from gemini.ts continue to work
• Test the changes to ensure functionality is preserved
• Run linting and type checking to ensure no compilation errors
• Test build process to ensure everything compiles correctly

Files modified:

• package.json - Updated dependency from @google/generative-ai to @google/genai
• app/actions/gemini.ts - Complete API migration to new package with extracted parameters
• app/actions/questionExample.ts - Updated response handling for new API
• app/actions/chatActions.ts - Updated response handling for new API

Key changes:

1. Package upgrade: Moved from deprecated @google/generative-ai v0.24.1 to current @google/genai v1.21.0
2. Model upgrade: Updated from gemini-1.5-flash to gemini-2.5-flash
3. API structure change:
   • Old: new GoogleGenerativeAI().getGenerativeModel().generateContent()
   • New: new GoogleGenAI().models.generateContent()
4. Response handling:
   • Old: result.response.text()
   • New: result.text (with proper null checks)
5. Proxy configuration: Updated to use httpOptions.baseUrl for the proxy fallback
6. Parameter extraction: Extracted model and contents into a reusable params variable, similar to the original ModelParams pattern, making it easier to modify parameters and reducing code duplication

All TypeScript compilation, linting, and build processes pass successfully.

Original prompt

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This section details on the original issue you should resolve

<issue_title>gemini-1.5-flashと@google/generative-aiはdeprecated</issue_title>
<issue_description>gemini-1.5-flash → gemini-2.5-flashに、
@google/generative-ai → @google/genai に移行する必要がある。</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #39

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
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