Replace legacy *.grails.org URLs with their canonical grails.apache.org targets

[jamesfredley]

Summary

The Plugins link in the site header pointed at https://plugins.grails.org, which is kept alive only as a meta-refresh redirect back to https://grails.apache.org/plugins.html. Many other links across guides, blog posts, and the shared chrome had the same shape - they targeted a legacy *.grails.org host that exists today only to bounce visitors to the canonical grails.apache.org URL. Each redirect costs the user an extra hop, hurts SEO, and breaks if the legacy hosts ever go away.

This PR replaces every redirect-bound URL in the source tree with its canonical grails.apache.org destination so internal links resolve directly.

239 files changed, 358 insertions(+), 358 deletions(-) - a strict 1-for-1 URL swap (no content rewriting).

Concrete fix the user asked for

Before:

<li><a href='https://plugins.grails.org'>Plugins</a></li>

After:

<li><a href='https://grails.apache.org/plugins.html'>Plugins</a></li>

Verified in build/dist/index.html line 92 after running ./gradlew build.

URL mapping applied

Old (redirects back to grails.apache.org)	New (canonical)
plugins.grails.org	grails.apache.org/plugins.html
guides.grails.org<path>	grails.apache.org/guides<path> (path-preserving)
docs.grails.org<path>	grails.apache.org/docs<path> (path-preserving)
views.grails.org/*	grails.apache.org/docs/latest/guide/theWebLayer.html#gson
async.grails.org/*	grails.apache.org/docs/latest/guide/async.html
testing.grails.org/*	grails.apache.org/docs/latest/guide/testing.html
gsp.grails.org/*	grails.apache.org/docs/latest/guide/theWebLayer.html#gsp
grails.org/<X>.html	grails.apache.org/<X>.html
grails.org/learn.html	grails.apache.org/learning.html (page renamed)
grails.org/plugin/<X>	grails.apache.org/plugins.html (legacy 404)
grails.org/blog<path>	grails.apache.org/blog<path>
grails.org/ and bare grails.org	grails.apache.org/
www.grails.org<path>	grails.apache.org<path>

The four subdomains views/async/testing/gsp.grails.org are mapped to the equivalent anchor on the canonical site because the legacy paths are dropped at redirect time anyway.

Intentionally NOT touched

• gorm.grails.org/* - some paths (notably /latest/neo4j/manual/...) have no canonical replacement on grails.apache.org because GORM for Neo4j has not been updated for Grails 7/8. The gorm.grails.org URL is still the current canonical destination for those readers.
• start.grails.org, slack.grails.org, repo.grails.org, prev-snapshot.grails.org - canonical hosts that serve content directly (Forge, Slack signup, JFrog Maven repo, Grails 8 snapshot Forge).
• grails.org/buildstatus.html - redirects to a GitHub README, not back to grails.apache.org, so it falls outside the redirect-back-to-here scope of this change.
• buildSrc/src/test/resources/parity-baseline/ - golden HTML snapshot of the legacy site, used by ParityCheckGuideTask as a regression-test fixture; rewriting it would corrupt the source-of-truth the renderer is diffed against.
• Buildscripts that intentionally reference guides.grails.org as the legacy base for the redirect-stub generator and parity baseline: AdHocFixtureDiff.groovy, GenerateRedirectsManifestTask.groovy, GenerateRedirectStubsTask.groovy, ParityCheckGuideTask.groovy, StructuralDiffGuidesTask.groovy.
• README.md and buildSrc/VENDOR.md - both document the migration itself.
• minutes/20210321-tab.md - frozen TAB historical record.

How it was done

A repeatable Groovy script walked the source tree applying ordered regex replacements (kept in C:\Users\james\AppData\Local\Temp\opencode\rewrite-redirect-links.groovy while writing this PR). The script also emitted an inventory of every *.grails.org reference it deliberately left untouched so reviewers can sanity-check the skip list.

Files changed by directory

Directory	Files
guides/	228
posts/	6
buildSrc/	4 (kapa.ai widget disclaimer in chrome HTML)
templates/	1 (the header)

Verification

• ./gradlew validateGuides -PvalidationMode=both -> 93 guides parsed, 0 errors
• ./gradlew build -> renderSite succeeds; rendered Plugins link in build/dist/index.html is now https://grails.apache.org/plugins.html

A final rg https?://[a-z0-9-]+\.grails\.org over the source tree shows the only remaining matches are in the explicitly-preserved files listed above.