Event instructors and contributors

[fbacall]

Summary of changes

• Allow contributors and instructors to be credited for events.
• Allows filtering/searching by these fields.
• Extracts from and serializes into the instructor and contributor fields of CourseInstance.

Motivation and context

#993

Screenshots

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Checklist

• I have read and followed the CONTRIBUTING guide.
• I confirm that I have the authority necessary to make this contribution on behalf of its copyright owner and agree to license it to the TeSS codebase under the BSD license.

[Copilot]

Pull request overview

Adds first-class support for crediting event contributors and instructors, and exposes these roles through search/facets and Bioschemas CourseInstance JSON-LD output (aligned with issue #993).

Changes:

• Adds contributors and instructors person-role associations to Event, including Solr indexing + facet support.
• Extends the event form and extra-metadata display to edit/show these roles.
• Serializes contributors/instructors into the Bioschemas CourseInstance generator and updates/expands tests accordingly.

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
test/models/event_test.rb	Adds model-level tests for assigning contributors/instructors from hashes and Person objects.
test/integration/bioschemas_test.rb	Verifies contributors/instructors appear correctly in generated Bioschemas/RDF output.
lib/bioschemas/course_instance_generator.rb	Emits schema:contributor and schema:instructor from event people roles.
app/views/events/_form.html.erb	Adds form sections to edit contributors and instructors via shared people form partial.
app/views/common/_extra_metadata.html.erb	Displays instructors in the extra metadata block.
app/views/bioschemas/_preview_button.html.erb	Minor styling change (adds mt-3 class) to preview form.
app/models/event.rb	Introduces HasPeople + has_person_role for contributors/instructors; adds Solr fields and facets.
app/controllers/events_controller.rb	Permits contributors/instructors in strong params.
Gemfile.lock	Updates TeSS_RDF_Extractors git revision and bumps nokogiri patch version.

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