Merge syntax-highlighting branch: add syntax highlighting and intra-line diff

- Syntax highlighting for markdown code blocks, read/write tool output
- Intra-line diff highlighting for edit tool with word-level inverse
- VS Code-style syntax colors in themes
- Fix Google provider FinishReason handling
- Upgrade @google/genai to 1.34.0

packages/coding-agent/package.json

@@ -43,6 +43,7 @@
 		"@mariozechner/pi-ai": "^0.23.3",
 		"@mariozechner/pi-tui": "^0.23.3",
 		"chalk": "^5.5.0",
+		"cli-highlight": "^2.1.11",
 		"diff": "^8.0.2",
 		"file-type": "^21.1.1",
 		"glob": "^11.0.3",