feat!: adopt mod-utils v6 (mod-leaflet v3)

[markdumay]

Summary

• Bump the module's own Go path from /v2 to /v3 and require
  github.com/gethinode/mod-utils/v6 v6.0.1 (never v6.0.0, which carries a known camelKey
  defect).
• Migrate the module's sole InitArgs.html call site to the clean Args.html API.
• Update config.toml and exampleSite/hugo.toml module import paths and re-vendor.

Part of the mod-utils v6 adoption program: gethinode/mod-utils#334. See the mod-utils README
"Argument validation" section for the v5-to-v6 migration notes (separated envelope,
defaulted list, warnings-first rollout for the InitArgs.html/InitTypes.html shims).

Migrated call sites

• layouts/shortcodes/map.html — the only InitArgs.html call site in the module. Switched to
  partial "utilities/Args.html" (dict "structure" "map" "args" .Params "named" .IsNamedParams "group" "shortcode" "strict" false). strict: false because this is a user-facing shortcode
  (site-authored content). Access is via the separated $result.args envelope; $error is now
  set from $result.err. No dual kebab/camel handling, _default plumbing, or or-based
  falsy-fallback workarounds were present to remove — the one existing | default fallback
  ($args.id | default (printf "leaflet-map-%d" .Ordinal)) is a computed ID default that has no
  static default in the schema, so it is not the "explicit false/0 gets swallowed" hazard the
  program's standing checklist item targets and was left as-is.

Verification (recipe step 5)

• hugo mod graph -s exampleSite (workspace-file exampleSite, per this module's wiring): shows
  github.com/gethinode/mod-leaflet/v3 github.com/gethinode/mod-utils/v6@v6.0.1+vendor only —
  no mod-utils/v5 anywhere in the graph.
• pnpm test (pnpm build → clean, vendor, hugo --gc --minify -s exampleSite) exits 0. Zero
  ERROR lines. The only WARN lines are pre-existing Hugo deprecations unrelated to this module
  (languageCode, .Site.Data) — zero warnings attributable to the map shortcode.
• The exampleSite's existing content (exampleSite/content/_index.md) already exercises the
  map shortcode with real arguments (class, lat, long, popup, popup-lat,
  popup-long, plus the zoom/id defaults) — not a placeholder, so no demo-content seeding
  was needed for the exercise gate.
• HTML-source diff (recipe pilot refinement 5): captured exampleSite/public/index.html before
  and after the migration (via git stash/pop around a clean rebuild) — byte-identical.
• Visual regression (own exampleSite, tests/visual/visual.mjs from the Hinode program
  workspace): baseline shot from the pristine clone before any change, candidate shot after.
  compare result: 3 pages compared, 0 flagged, 0.0000% diff ratio on every page
  (categories, index, tags). Map tile areas are masked by the harness by design (external
  tiles, non-localhost requests blocked) — the byte-identical HTML diff covers that gap.

Evidence

• New path: github.com/gethinode/mod-leaflet/v3
• hugo mod graph v6-only line: github.com/gethinode/mod-leaflet/v3 github.com/gethinode/mod-utils/v6@v6.0.1+vendor
• Build exit code: 0 (zero ERROR lines)
• Migrated call sites: layouts/shortcodes/map.html (1 of 1)
• Warning triage: no warnings attributable to the module; 2 pre-existing unrelated Hugo
  deprecation warnings observed and left untouched (out of scope)
• Visual diff triage: 0 flagged / 3 pages, 0.0000% diff — no re-baseline needed

🤖 Generated with Claude Code

[markdumay]

🎉 This PR is included in version 3.0.0 🎉

The release is available on GitHub release

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