mcp: Fix source property showing up as undefined in settings (#43417)

Follow up to #39021.

<img width="576" height="141" alt="image"
src="https://github.com/user-attachments/assets/c89885a4-e664-4614-9bb0-86442dff34ee"
/>

- Add migration to remove `source` tag because `ContextServerSettings`
is now untagged
- Fix typos in context server modal
- PR seems to have removed the `test_action_namespaces` test, which I
brought back in this PR

Release Notes:

- Fixed an issue where the `source` property of MCP settings would show
up as unrecognised

docs/src/ai/mcp.md

@@ -40,12 +40,12 @@ You can connect them by adding their commands directly to your `settings.json`,
 ```json [settings]
 {
   "context_servers": {
-    "run-command": {
+    "local-mcp-server": {
       "command": "some-command",
       "args": ["arg-1", "arg-2"],
       "env": {}
     },
-    "over-http": {
+    "remote-mcp-server": {
       "url": "custom",
       "headers": { "Authorization": "Bearer <token>" }
     }