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.

tests/unit/app-menu.test.ts

@@ -21,6 +21,7 @@ const state = vi.hoisted(() => ({
 }))
 vi.mock("@/electron/main/config-manager", () => ({
     applyPresetToEnv: (id: string) => {
+        if (id === "missing") return null
         state.current = id
         return { AI_PROVIDER: id }
     },
@@ -80,4 +81,24 @@ describe("switchPreset", () => {
         await third
         expect(state.current).toBe("B")
     })
+
+    it("does not bring back the old preset over a deletion", async () => {
+        const toB = switchPreset("B").catch(() => {})
+        // B is deleted while its restart is pending
+        state.current = null
+        state.restarts[0].reject(new Error("timed out"))
+        await toB
+        expect(state.current).toBeNull()
+        expect(state.restarts).toHaveLength(1)
+    })
+
+    it("still rolls back when a later request named no preset", async () => {
+        const toB = switchPreset("B").catch(() => {})
+        await expect(switchPreset("missing")).rejects.toThrow("not found")
+        state.restarts[0].reject(new Error("timed out"))
+        await new Promise((r) => setTimeout(r, 0))
+        state.restarts[1]?.resolve()
+        await toB
+        expect(state.current).toBe("A")
+    })
 })