chore: remove dead code and unused dependencies

- Delete 4 unused files detected by knip
- Remove lint-staged, eslint-config-prettier, plausible-tracker
- Clean up knip.json entry patterns

knip.json

@@ -5,10 +5,6 @@
 		"src/app/**/layout.{ts,tsx}",
 		"src/app/**/route.{ts,tsx}",
 		"src/app/**/{error,not-found,loading,template,default,global-error}.{ts,tsx}",
-		"src/app/**/actions.{ts,tsx}",
-		"next.config.ts",
-		"src/proxy.ts",
-		"src/instrumentation.ts",
 		"sentry.{server,edge}.config.ts"
 	],
 	"project": ["src/**/*.{ts,tsx}"],