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/env-loader.test.ts

@@ -28,6 +28,8 @@ const KEYS = [
     "T_ESC_HASH",
     "T_ESC_INNER",
     "T_ESC_COMMENT",
+    "T_DIR",
+    "T_DIR_COMMENT",
 ]
 afterEach(() => {
     for (const k of KEYS) delete process.env[k]
@@ -92,4 +94,18 @@ describe("loadEnvFile", () => {
         expect(process.env.T_ESC_INNER).toBe('a # \\"b\\"')
         expect(process.env.T_ESC_COMMENT).toBe('x\\"y')
     })
+
+    it("keeps a backslash before the closing quote, like dotenv", () => {
+        dir.path = mkdtempSync(join(tmpdir(), "env-loader-"))
+        writeFileSync(
+            join(dir.path, ".env"),
+            ['T_DIR="C:\\dir\\"', 'T_DIR_COMMENT="C:\\data\\" # dir'].join(
+                "\n",
+            ),
+        )
+        loadEnvFile()
+        // Windows folders; dotenv 16.6.1 reads them the same
+        expect(process.env.T_DIR).toBe("C:\\dir\\")
+        expect(process.env.T_DIR_COMMENT).toBe("C:\\data\\")
+    })
 })