server: use a src directory for sanity

deno.json

···
 {
   "tasks": {
-    "dev": "PORT=8000 deno run --watch --allow-net --allow-env=HOSTNAME,PORT,NODE_ENV main.ts"
+    "dev": "PORT=8000 deno run --watch --allow-net --allow-env=HOSTNAME,PORT,NODE_ENV src/index.ts"
   },
   "imports": {
     "@atcute/identity-resolver": "npm:@atcute/identity-resolver@^1.1.3"

root.ts src/root.ts

···
-import index from "./index/index.html" with { type: "text" };
+import index from "./www/index.html" with { type: "text" };
 
 export default function (req: Request) {
   if (new URL(req.url).pathname === "/")