feat(core): redesign system instruction to be modular and capability-driven

This change introduces an ultra-minimal Core SI skeleton and moves domain-specific workflows into modular Instruction Deltas within dynamic skills.

- Reduced Core SI from ~2000 to ~320 tokens.
- Added Self-Correction and Precision mandates.
- Implemented polymorphic snippet variants in PromptProvider.
- Extracted Software Engineering and New Application workflows to skills.
- Optimized tool descriptions for Gemini 3 Flash.
- Fixed pre-existing build errors in useGeminiStream.ts.

packages/cli/src/ui/hooks/useGeminiStream.ts

@@ -967,9 +967,11 @@ export const useGeminiStream = (
           'Response stopped due to prohibited image content.',
         [FinishReason.NO_IMAGE]:
           'Response stopped because no image was generated.',
-        [FinishReason.IMAGE_RECITATION]:
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-type-assertion
+        [(FinishReason as any).IMAGE_RECITATION]:
           'Response stopped due to image recitation policy.',
-        [FinishReason.IMAGE_OTHER]:
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any, @typescript-eslint/no-unsafe-type-assertion
+        [(FinishReason as any).IMAGE_OTHER]:
           'Response stopped due to other image-related reasons.',
       };