docs(app): add dedicated Troubleshooting page

[benjaminach]

This PR reorganizes the troubleshooting documentation to make first deployment
issues easier to identify and route to the right detailed page.

Main changes:

• Move application troubleshooting content into a dedicated
  platform/app/troubleshooting section.
• Replace the former broad Common Deployment Errors page with more focused
  pages:
  • Deployment Issues for source fetching, technology detection, and build
    failures.
  • Boot Errors for start, timeout, and postdeploy hook errors.
  • Runtime Issues for problems happening after the app is running.
• Rename and move the former Application Crash page into the new runtime
  troubleshooting section.
• Add shared language start-page links through a reusable include.
• Update related links from Getting Started, Procfile, postdeploy hook, CLI,
  and container management pages.

Why

The previous structure mixed several troubleshooting phases in pages that were
hard to scan and not always clearly named. This change separates deployment,
startup, and runtime issues so users can first identify where the failure
happens, then follow the relevant detailed guide.

Notes

• The old common-deployment-errors page is intentionally removed.
• Existing redirect entries were left untouched; new redirects were appended at
  the end of the 301 section.

---

This PR continues the work initiated by @sc-zenokerr in #3485.

[benjaminach]

From the current draft, I already know that @Frzk does not like the "Quick Resolution Guide" in the "Getting Started" section.

Since "Common deployment errors" have been moved to the dedicated "Troubleshooting" section, I chose to keep a page in "Getting Started" to help customers understand the stack and identify common sources of issues.

If we decide not to keep this "Quick Resolution Guide", we can still remove it from that section.

[SC-Samir]

The PR is ready for review or still in draft?

[benjaminach]

The PR is ready for review or still in draft?

Ready for review 👌 Thanks

[Frzk]

@benjaminach: I've just pushed the new Jekyll tag in this branch, so you may want to wait until I can put it on all concerned pages?

[semgrep-code-scalingo]

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MPL-2.0

• lightningcss-android-arm64 1.31.1
• lightningcss-darwin-arm64 1.31.1
• lightningcss-darwin-x64 1.31.1
• lightningcss-freebsd-x64 1.31.1
• lightningcss-linux-arm-gnueabihf 1.31.1
• lightningcss-linux-arm64-gnu 1.31.1
• lightningcss-linux-arm64-musl 1.31.1
• lightningcss-linux-x64-gnu 1.31.1
• lightningcss-linux-x64-musl 1.31.1
• lightningcss-win32-arm64-msvc 1.31.1
• lightningcss-win32-x64-msvc 1.31.1

[Frzk]

• I feel like the new Troubleshooting pages are great, but maybe lack a bit of polish/homogeneity pass. This can come later.
• Not found of the "Quick Resolution" page (more below)
• A very little nitpicky, non-blocking suggestion.

[benjaminach]

• I feel like the new Troubleshooting pages are great, but maybe lack a bit of polish/homogeneity pass. This can come later.

In this pass I tried to limit changes to the structuration of the pages, but indeed, we will have to rework the content a bit further.

[EtienneM]

praise: I love the timeline 🤩

praise: thanks a lot for this refacto

I just added a bunch of suggestions, but already approving.