docs: fix locale-mismatched Quickstart links in 3 introduction pages

[Jeff-Kazzee]

The Introduction pages for Indonesian (id), Persian (fa), and Traditional Chinese (zh-tw) currently link readers to the English Quickstart instead of their own locale's Quickstart.

All three locales already have full, current Quickstart pages (id: 2493 bytes / fa: 3146 bytes / zh-tw: 2411 bytes — each fully translated, referencing Go 1.25). The link target just wasn't updated when those Quickstart pages were authored.

Source evidence

In the markdown source at HEAD of master, the link target in each affected file was https://gin-gonic.com/en/docs/quickstart/:

src/content/docs/id/docs/introduction/index.md:11
src/content/docs/fa/docs/introduction/index.md:11
src/content/docs/zh-tw/docs/introduction/index.md:11

Per-locale link table (after this PR)

All 12 locale Introduction pages now link to their own locale's Quickstart:

Locale	Introduction → Quickstart link
en	gin-gonic.com/en/docs/quickstart/
es	gin-gonic.com/es/docs/quickstart/
pt	gin-gonic.com/pt/docs/quickstart/
ko-kr	gin-gonic.com/ko-kr/docs/quickstart/
zh-cn	gin-gonic.com/zh-cn/docs/quickstart/
ru	gin-gonic.com/ru/docs/quickstart/
ja	gin-gonic.com/ja/docs/quickstart/
ar	gin-gonic.com/ar/docs/quickstart/
tr	gin-gonic.com/tr/docs/quickstart/
id	gin-gonic.com/id/docs/quickstart/ ← fixed
fa	gin-gonic.com/fa/docs/quickstart/ ← fixed
zh-tw	gin-gonic.com/zh-tw/docs/quickstart/ ← fixed

Style convention

Preserves the existing absolute-URL pattern used in the 9 already-correct locale Introduction files. Matches the convention applied in the upstream fix for gin-gonic/gin#4214.

Why this isn't an intentional fallback

The locale Quickstart pages already existed at or before the affected Introduction pages' current upstream versions:

Locale	Quickstart last touched	Introduction last touched before this PR
id	d0b8ed1 on 2026-04-02	4ef9b72 on 2026-04-29
fa	8a61f8a on 2026-03-14	8a61f8a on 2026-03-14
zh-tw	8a61f8a on 2026-03-14	8a61f8a on 2026-03-14

So these were not English fallbacks waiting for missing locale Quickstart pages. The target pages were already present.

Repro from source

1. Clone master.
2. Run grep -nE 'gin-gonic\.com/[a-z-]+/docs/quickstart' src/content/docs/<locale>/docs/introduction/index.md for each locale.
3. Observe that before this PR, id, fa, and zh-tw matched /en/docs/quickstart/; all others self-match.

Diff

3 lines, 3 files — one URL substitution per file.

AI assistance

This change was drafted with AI assistance. Verification (per-locale link table, target-file existence checks, commit-date analysis) was reproduced on a clean clone of master. No open PR addresses these files.