fix: what the batch C review found

- A redirect followed for a custom base URL (quota on) no longer carries
  the user's key or cookies to another origin, as fetch itself does, and
  a private address may redirect to another private one (already counted).
- The admin Test of an Ollama or Vertex AI entry without a URL goes where
  chat sends that entry's key: the environment's own URL variable, for
  Ollama else the local default. The Test of an Ollama Cloud key without
  a URL went to the cloud while chat went to local Ollama.
- Chat saves: each save notes the chat on screen and the order of the
  reads before reading its data. A save read before switching chats no
  longer writes into the chat switched to, and a copy that waited for its
  thumbnail no longer replaces a newer one.
- "Continue without saving" keeps its button when a later auto-save fails,
  and goes away when a new message is sent.
- A screenshot check that was waiting for its image when the user pressed
  Stop stays skipped after the next message.
- MCP History: draw.io's own copy of a diagram (after get_diagram) no
  longer adds an entry without a picture; a change of background is still
  its own version. The tab ignores an edit's answer that arrives after a
  newer AI write loaded.
- Desktop: a deleted preset is not brought back by a failed switch, and a
  request naming no preset does not stop a rollback. An origin keeping
  an access code counts as having settings.
- .env: a quoted value ending in a backslash ("C:\dir\") is read as dotenv
  reads it.
- The tool card no longer crashes on an id that does not turn into text;
  an older Test's success timer no longer ends a newer Test's spinner.
- Tests that passed without their fix now check it.

packages/mcp-server/tests/http-server.test.ts

@@ -582,6 +582,15 @@ describe("history restore", () => {
         expect(getHistory(id)).toHaveLength(1)
         // The missing image is filled in
         expect(getHistory(id)[0].svg).toBe("SVG")
+        // draw.io's copy of it, as a sync reply brings it back
+        addHistory(
+            id,
+            page("same").replace(
+                "<mxGraphModel>",
+                '<mxGraphModel dx="1244" dy="534" grid="1" pageWidth="850">',
+            ),
+        )
+        expect(getHistory(id)).toHaveLength(1)
     })
 
     it("keeps a version that changed only the background", () => {