Enable getting started translations (#21842)

## Summary

The Getting Started pages on the docs site (docs.twenty.com) were only
ever available in English, never translated into the other supported
languages.

**Root cause:** The Getting Started section (added in #19728) was never
added to the Crowdin source config (`crowdin-docs.yml`), so its `.mdx`
files were never uploaded for translation. Only `user-guide`,
`developers`, and `twenty-ui` were configured.

This also surfaced a related bug: because the pages had no translations,
the navigation generator fell back to the English page path for every
language, duplicating paths like `getting-started/introduction` across
all 14 language navs. Mintlify treats duplicate cross-language paths as
undefined behavior, which broke the language switcher (it always
redirected to `/getting-started/introduction`).

## Changes

- `.github/crowdin-docs.yml` — add `getting-started/**/*.mdx` as a
translation source so the pages get sent to Crowdin.
- `packages/twenty-docs/scripts/fix-translated-links.sh` — add
`getting-started` link-rewriting rules to match the other sections.
- `packages/twenty-docs/scripts/generate-docs-json.ts` — only include a
page in a non-default language when its translated file exists; drop
empty groups/tabs (removes the duplicate cross-language paths that broke
the switcher).
- `packages/twenty-docs/docs.json` — regenerated.



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Co-authored-by: Cursor <cursoragent@cursor.com>

.github/crowdin-docs.yml

@@ -9,6 +9,10 @@
 "base_path": ".."
 
 files: [
+  {
+    "source": "packages/twenty-docs/getting-started/**/*.mdx",
+    "translation": "packages/twenty-docs/l/%two_letters_code%/getting-started/**/%original_file_name%",
+  },
   {
     #
     # MDX documentation files - user-guide