Fix mdx bundler import (#15794)

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## DESCRIBE YOUR PR
This PR fixes a regresses introduced in
#15452

The platform-redirect page was failing in production with: "Cannot find
module 'mdx-bundler'"

Update `docTree.ts` to import from `frontmatter.ts` instead of `mdx.ts`.
At runtime, these functions only read from pre-computed doctree.json
files, so mdx-bundler is not needed.

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Author: jaffrepaul

.github/workflows/lint-404s.yml

@@ -23,6 +23,7 @@ jobs:
               - 'docs/**'
               - 'includes/**'
               - 'platform-includes/**'
+              - 'scripts/lint-404s/**'
             dev-docs:
               - 'develop-docs/**'
       - uses: oven-sh/setup-bun@v2

docs/concepts/key-terms/key-terms.mdx

@@ -62,6 +62,6 @@ Each of these key features have their own page (or set of pages) in the [sentry.
 
 - **Alerts** - Where you can create new alert rules and manage existing ones. Learn more in the full [Alerts documentation](/product/alerts/).
 
-- **Dashboards** - Provide you with a broad overview of your application’s health by allowing you to navigate through error and performance data across multiple projects. Dashboards are made up of one or more widgets, and each widget visualizes one or more **Discover** or **Issues** queries. Learn more in the full [Dashboards documentation](/product/dashboards/).
+- **Dashboards** - Provide you with a broad overview of your application's health by allowing you to navigate through error and performance data across multiple projects. Dashboards are made up of one or more widgets, and each widget visualizes one or more **Discover** or **Issues** queries. Learn more in the full [Dashboards documentation](/product/dashboards/).
 
 - **Releases** - Provides a high-level view of each release version, the associated project, the adoption stage of each release, the authors of each commit, as well as release health data including the percentage of crash-free users, and the percentage of crash-free sessions. You can navigate directly to the **Releases** page or from the **Issue Details** page, by selecting release ID listed under "Last Seen". Learn more in the full [Releases documentation](/product/releases/).

src/docTree.ts

@@ -1,5 +1,5 @@
+import {getDevDocsFrontMatter, getDocsFrontMatter} from './frontmatter';
 import {isDeveloperDocs} from './isDeveloperDocs';
-import {getDevDocsFrontMatter, getDocsFrontMatter} from './mdx';
 import {platformsData} from './platformsData';
 import {
   FrontMatter,