feat: Story 11 - Left-align text and add syntax highlighting

Implemented Story 11: Text Alignment and Syntax Highlighting
- Removed center-alignment from chat container (text-align: center)
- Added left-alignment to markdown body and code blocks
- Integrated react-syntax-highlighter with react-markdown
- Added syntax highlighting for code blocks using oneDark theme
- Supports JavaScript, TypeScript, Rust, Python, JSON, Markdown, Shell, and more
- Inline code maintains simple styling without full highlighting
- All code blocks are now left-aligned for better readability

Fixed: Agent over-aggressive file writing behavior
- Refined system prompt to distinguish between:
  * 'show/example/how does' → respond with code in chat
  * 'create/add/implement/fix' → use write_file tool
- Removed aggressive AGENT DIRECTIVE prefix from user messages
- Softened reminder message to reflect nuanced behavior
- Agent can now both teach (show examples) and implement (write files)

Updated Specs
- Added Text Alignment and Readability section to UI_UX.md
- Added Syntax Highlighting section with implementation details
- Updated SDSW workflow: acceptance criteria marked complete only after user acceptance

Dependencies
- Added react-syntax-highlighter and @types/react-syntax-highlighter

package.json

@@ -15,21 +15,23 @@
     "@tauri-apps/plugin-dialog": "^2.4.2",
     "@tauri-apps/plugin-opener": "^2",
     "@tauri-apps/plugin-store": "^2.4.1",
+    "@types/react-syntax-highlighter": "^15.5.13",
     "react": "^19.1.0",
     "react-dom": "^19.1.0",
-    "react-markdown": "^10.1.0"
+    "react-markdown": "^10.1.0",
+    "react-syntax-highlighter": "^16.1.0"
   },
   "devDependencies": {
     "@tauri-apps/cli": "^2",
+    "@testing-library/jest-dom": "^6.0.0",
+    "@testing-library/react": "^14.0.0",
+    "@testing-library/user-event": "^14.4.3",
     "@types/react": "^19.1.8",
     "@types/react-dom": "^19.1.6",
     "@vitejs/plugin-react": "^4.6.0",
-    "typescript": "~5.8.3",
-    "vite": "^7.0.4",
     "jest": "^29.0.0",
     "ts-jest": "^29.0.0",
-    "@testing-library/react": "^14.0.0",
-    "@testing-library/jest-dom": "^6.0.0",
-    "@testing-library/user-event": "^14.4.3"
+    "typescript": "~5.8.3",
+    "vite": "^7.0.4"
   }
 }