Syntax highlighting improvements

- Fix cli-highlight import (use static import instead of dynamic require)
- Add syntax highlighting to read/write tool output
- Update dark/light themes with VS Code default syntax colors
- Add highlightCode and getLanguageFromPath exports
- Upgrade @google/genai to 1.34.0 for IMAGE_RECITATION/IMAGE_OTHER FinishReason
- Add AGENTS.md rule: never downgrade code to fix type errors from outdated deps

packages/coding-agent/src/modes/interactive/theme/dark.json

@@ -51,15 +51,15 @@
 		"toolDiffRemoved": "red",
 		"toolDiffContext": "gray",
 
-		"syntaxComment": "gray",
-		"syntaxKeyword": "cyan",
-		"syntaxFunction": "blue",
-		"syntaxVariable": "",
-		"syntaxString": "green",
-		"syntaxNumber": "yellow",
-		"syntaxType": "cyan",
-		"syntaxOperator": "",
-		"syntaxPunctuation": "gray",
+		"syntaxComment": "#6A9955",
+		"syntaxKeyword": "#569CD6",
+		"syntaxFunction": "#DCDCAA",
+		"syntaxVariable": "#9CDCFE",
+		"syntaxString": "#CE9178",
+		"syntaxNumber": "#B5CEA8",
+		"syntaxType": "#4EC9B0",
+		"syntaxOperator": "#D4D4D4",
+		"syntaxPunctuation": "#D4D4D4",
 
 		"thinkingOff": "darkGray",
 		"thinkingMinimal": "#6e6e6e",