fix(webui): missing HTTP method on fetch calls with body

6 call sites used the fetch default GET while sending a request body,
which browsers reject outright ('Request with GET/HEAD method cannot
have body'). Affected flows: create key, save source, save auto rules,
upload adapter, update key model scope, and /api/chat streaming.

All now send the method their backend handlers require (POST or PUT)
with an explicit Content-Type.

internal/gateway/ui/index.html

@@ -2268,6 +2268,7 @@
           firstChunk = Date.now();
         try {
           const resp = await fetch("/api/chat", {
+            method: "POST",
             headers: { "Content-Type": "application/json" },
             body: JSON.stringify({
               model,
@@ -2516,6 +2517,8 @@
         btn.disabled = true;
         try {
           await api("/api/sources", {
+            method: "POST",
+            headers: { "Content-Type": "application/json" },
             body: JSON.stringify(payload),
           });
           toast(t("toastSaved"));
@@ -3114,6 +3117,8 @@
           }),
         );
         await api("/api/auto", {
+          method: "PUT",
+          headers: { "Content-Type": "application/json" },
           body: JSON.stringify({ rules }),
         });
       }
@@ -3372,6 +3377,8 @@
         if (!name || !code) return toast(t("toastNeedAll"));
         try {
           await api("/api/adapters", {
+            method: "POST",
+            headers: { "Content-Type": "application/json" },
             body: JSON.stringify({ name, code }),
           });
           toast(t("toastUploaded"));
@@ -3584,6 +3591,8 @@
       }
       async function putScope(key, scopes) {
         await api("/api/keys/" + encodeURIComponent(key), {
+          method: "PUT",
+          headers: { "Content-Type": "application/json" },
           body: JSON.stringify({ models: scopes }),
         });
       }
@@ -3905,6 +3914,8 @@
         let j;
         try {
           j = await api("/api/keys", {
+            method: "POST",
+            headers: { "Content-Type": "application/json" },
             body: JSON.stringify({
               name,
               role: $("#kc-role").value,