Port DefinedTerm keyword fix (#219) from master into dev

[ywkim312]

Summary

Port the DefinedTerm keyword rendering fix from master (#219) into dev, so BODC-style keyword objects display as names/links instead of broken object output.

This does not re-apply #279 / fix/278 (Docker/Vue peer-dependency fix). dev already has Vue 3.5 and a yarn-based Dockerfile.

@valentinedwv This change is already on master via #219. Bringing it into dev now should reduce the chance of losing the DefinedTerm keyword fix (or hitting a painful conflict) later when we merge dev → master.

#279 / the Docker+Vue fix is intentionally not included here — dev already has that stack.

Since you already reviewed/approved #219 on master, a quick re-approve + merge of this PR into dev would be appreciated. Thanks!

Changes

• Update dataset.vue to handle string and DefinedTerm keywords (name + optional URL)
• Add providers rendering support from #219
• Update Blazegraph SPARQL keyword patterns to support literal keywords and DefinedTerm name
• Add config_qlever_test.yaml
• Allow env overrides for local API_URL / JSONLD_PROXY in development.js
• Ignore root .env in .gitignore

Test plan

• Open a dataset with DefinedTerm keywords and confirm names render (and links when URL/@id exists)
• Confirm plain string keywords still render normally
• Confirm providers section renders when provider data exists
• Confirm no Dockerfile / package.json / yarn.lock changes in this PR