Switch Docsy theme to Hugo Modules and unblock Hugo 0.161 upgrade

[brooke-hamilton]

Summary

Replaces the vendored copy of the Docsy theme with a Hugo Modules import, and brings the Hugo CLI bump from #98 along for the ride.

This unblocks the failing CI build on #98. Once this PR merges, #98 can be closed (its hugo-extended bump is included here as the first commit on this branch).

Why CI was failing on #98

PR #98 bumps hugo-extended from ^0.102.3 to ^0.161.1. Hugo 0.161 removed the internal template _internal/google_analytics_async.html (deprecated in v0.123 — it was the snippet for legacy UA-... Analytics IDs; only the G-... GA4 variant remains). The vendored Docsy in radblog/themes/docsy/layouts/partials/head.html still referenced that template in its else branch, so the build errored:

ERROR error building site: html/template:_partials/head.html:52:16:
no such template "_internal/google_analytics_async.html"

Patching the vendored file would work, but the underlying problem is that Docsy was checked in at repo bootstrap and never updated since (Docsy v0.6.0 → current v0.15.0). A stale .gitmodules entry pointed at a non-existent docs/themes/docsy submodule, and radblog/go.mod had a dangling github.com/google/docsy v0.6.0 // indirect requirement — suggesting a half-finished Hugo Modules conversion that this PR completes.

Changes

• radblog/config.toml — removed theme = "docsy"; added [module].imports for github.com/google/docsy and github.com/google/docsy/dependencies.
• radblog/go.mod / radblog/go.sum — hugo mod get -u upgraded Docsy v0.6.0 → v0.15.0 and added docsy/dependencies v0.7.2.
• Removed the entire vendored radblog/themes/docsy/ tree (~260 files); Hugo now pulls Docsy from the module cache.
• Removed the orphaned root .gitmodules (the submodule it declared has never existed in this repo).
• .github/workflows/blog.yaml — dropped the now-broken Install Docsy dependencies step (its working directory no longer exists) and the submodules: true checkout flag (no submodules in the repo).
• Includes the dependabot bump from deps(deps-dev): bump the all group across 1 directory with 2 updates #98: hugo-extended ^0.102.3 → ^0.161.1 in radblog/package.json and radblog/package-lock.json.

Dependabot already has a gomod ecosystem configured for /radblog in .github/dependabot.yml, so future Docsy releases will be picked up automatically.

Validation

Built locally with Hugo 0.161.1 extended:

npm run build           # hugo --minify           → 49 pages, 0 errors
npm run build:preview   # hugo --buildDrafts ...  → 49 pages, 0 errors

Verified GA4 still renders in public/index.html:

gtag/js?id=G-SZ71KL0YSK
googletagmanager

Two pre-existing deprecation warnings remain (out of scope, non-blocking):

• languageCode config key is deprecated in favor of locale.
• .Language.LanguageDirection used inside Docsy itself; will be fixed by a future Docsy release.

Follow-up

• Close deps(deps-dev): bump the all group across 1 directory with 2 updates #98 once this merges.

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