Update Jig docs for the move to voxpupuli/jig and refresh to current CLI

[miharp]

What

The Jig scaffolding tool moved from github.com/avitacco/jig to github.com/voxpupuli/jig. This updates every reference and brings the prose in line with Jig's current CLI. All command syntax was validated against the Jig source.

Changes

Repo move:

• Point all avitacco/jig links and the go install path at voxpupuli/jig.

Command / prose fixes (devkit/jig.md, modules_publishing.markdown):

• Fix invalid commands (jig module build, jig build build, jig module) to the actual jig build.
• Document the --skip-interview flag and its companion value flags on jig new module, plus the template-override precedence (--template-dir flag, then template_dir config key). The README's JIG_TEMPLATE_DIR env var does not reliably bind in the source, so it's intentionally left out.

Discoverability and naming:

• Point the PDK page's jig "alternative" entry at our own /ecosystem/latest/devkit/jig.html docs (keeping a repo link for source/releases) and capitalize the proper noun "Jig".
• Add a "see installation and usage" pointer from the DevKit components list to the Scaffolding page.
• Add a cross-collection "Scaffolding modules with Jig" entry to the core OpenVox Modules nav. Cross-collection links use absolute paths per CONTRIBUTING.

jig validate / test unit / update:

• migrating.md: map pdk update/validate/test unit to the jig commands, noting they wrap the underlying bundle exec calls (still need bundle install).
• linting.md: note jig validate runs validate + lint (not lint_fix).
• unit_testing.md: add the run command (jig test unit, wrapping bundle exec rake spec).

Validation

• Verified the full command/flag set against the Jig source.
• bundle exec jekyll build passes; spot-checked the cross-collection link, nav entry, and new command prose in the built site.

Closes #348