Keep panel requests on the app's server and bounded

panel_request resolved paths with a check for a leading //, but URL
parsing also reads /\host as another host, so it could request other
servers. It now resolves the path against the app's address, refuses
any other origin, matches refused routes decoded as well, and does not
follow redirects. Responses are capped at 64 MiB while reading, with a
deadline; held responses make room on arrival and expire by time only,
so a response being read keeps its parts.

The panel keeps converted images only for its build files, so live
camera frames no longer accumulate, and failed build loads are retried.
The dev server answers a malformed /panel/ path with 400 instead of
crashing.

build/panel.js

@@ -74,7 +74,14 @@ export function panelBuildPlugin({ outDir = PANEL_OUT_DIR } = {}) {
         const { readFile } = await import('node:fs/promises');
         const { extname, resolve, sep } = await import('node:path');
         const root = resolve(server.config.root, outDir);
-        const relative = decodeURIComponent(pathname.slice(PANEL_BASE.length));
+        let relative;
+        try {
+          relative = decodeURIComponent(pathname.slice(PANEL_BASE.length));
+        } catch {
+          res.statusCode = 400;
+          res.end('Bad path');
+          return;
+        }
         const file = resolve(root, relative || 'index.html');
         if (file !== root && !file.startsWith(root + sep)) return next();
         try {