docs: plugins, cloudflare, sdk, elements, database (#240)

* docs: added plugins docs, updated cloudflare docs

* updated cli help text

* added `systemEntity` and added docs on how to work with system entities

* docs: added defaults to cloudflare image plugin

* docs: updated sdk and elements

app/src/adapter/cloudflare/vite.ts

@@ -6,7 +6,7 @@ import { resolve } from "node:path";
  * Vite plugin that provides Node.js filesystem access during development
  * by injecting a polyfill into the SSR environment
  */
-export function devFsPlugin({
+export function devFsVitePlugin({
    verbose = false,
    configFile = "bknd.config.ts",
 }: {