refactor: remove legacy codebaseIndexOpenAiCompatibleModelDimension property

[daniel-lxs]

Description

This PR is blocking #3999

This PR removes the legacy codebaseIndexOpenAiCompatibleModelDimension property and standardizes on the generic codebaseIndexEmbedderModelDimension property throughout the codebase.

Changes Made

1. Backend Configuration (src/services/code-index/config-manager.ts):

• Removed migration logic that was converting the old property to the new one
• Cleaned up the getConfig() method to only use the generic property

2. Message Types (src/shared/WebviewMessage.ts):

• Removed the legacy codebaseIndexOpenAiCompatibleModelDimension property from the CodeIndexSettings interface
• The interface now only contains the generic codebaseIndexEmbedderModelDimension property

3. Webview Message Handler (src/core/webview/webviewMessageHandler.ts):

• Removed backward compatibility code that was setting both properties
• Now only sets the generic codebaseIndexEmbedderModelDimension property

4. UI Component (webview-ui/src/components/chat/CodeIndexPopover.tsx):

• Removed the legacy property from the component's interface and default settings
• Removed backward compatibility logic in the initialization
• Improved UI logic: The "Model Dimension" input field is now only shown for OpenAI-compatible providers where custom models might be used
• The dimension field is hidden for OpenAI, Ollama, and Gemini providers since their model dimensions are auto-detected

5. Test Files:

• Fixed duplicate property definitions in src/core/config/__tests__/importExport.spec.ts
• Updated all test files to use the generic property name

Testing

• ✅ All backend tests pass (config-manager.spec.ts, importExport.spec.ts)
• ✅ All UI tests pass (510 tests passed, 1 skipped)
• ✅ Type checking passes
• ✅ Linting passes

Verification

The codebase now consistently uses only codebaseIndexEmbedderModelDimension for all providers, eliminating the technical debt from the old provider-specific naming convention.

Benefits

1. Cleaner codebase: Removes unnecessary backward compatibility code
2. Better UX: The UI now intelligently shows/hides the dimension field based on provider
3. Maintainability: Single property name makes the code easier to understand and maintain
4. Future-proof: New providers can use the same generic property without special handling

---

Important

Refactor to remove legacy codebaseIndexOpenAiCompatibleModelDimension and standardize on codebaseIndexEmbedderModelDimension across the codebase.

• Configuration:
  • Removed codebaseIndexOpenAiCompatibleModelDimension from config-manager.ts.
  • Standardized on codebaseIndexEmbedderModelDimension for all providers.
• Message Types:
  • Updated WebviewMessage.ts to use codebaseIndexEmbedderModelDimension.
• UI Component:
  • Updated CodeIndexPopover.tsx to use codebaseIndexEmbedderModelDimension.
  • Improved UI logic to show/hide "Model Dimension" field based on provider.
• Tests:
  • Updated tests in config-manager.spec.ts and service-factory.spec.ts to reflect property changes.
• Misc:
  • Updated i18n files to reflect changes in error messages and configuration keys.

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[delve-auditor]

✅ No security or compliance issues detected. Reviewed everything up to 167a9e8.

Security Overview

• 🔎 Scanned files: 27 changed file(s)

Detected Code Changes

Change Type	Relevant files
Refactor	► config-manager.ts     Move embedding dimension to generic config ► service-factory.ts     Update vector dimension handling ► modes.ts     Simplify mode selection logic
Enhancement	► embeddings.json     Add new translation strings for service factory errors
Bug Fix	► reminder.ts     Remove default todo list message

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