Refactor LSP tools and add hover functionality

- Split diagnostics tool into separate lsp-diagnostics.ts file
- Add new lsp-hover.ts tool for LSP hover information
- Update tool exports and session integration
- Remove old diagnostics.ts file

🤖 Generated with opencode
Co-Authored-By: opencode <noreply@opencode.ai>

js/package.json

@@ -27,6 +27,7 @@
     "ai": "^5.0.0-alpha.4",
     "cac": "^6.7.14",
     "clipanion": "^4.0.0-rc.4",
+    "diff": "^8.0.2",
     "hono": "^4.7.10",
     "hono-openapi": "^0.4.8",
     "jsdom": "^26.1.0",