Add optional Project.display_short_name for compact artifact cards (#1156)

[jonfroehlich]

Closes #1156.

Problem

Publication / talk / video cards show the project's full name in the flask "View project" chip, which is long and noisy for projects with descriptive titles (e.g. "Multi-Stakeholder Interviews to Address Urban Accessibility").

The existing Project.short_name can't be used for this — it's the URL slug (lowercase, no spaces, e.g. projectsidewalk), not a reader-facing label.

Change

• New optional field Project.display_short_name — a short display label (e.g. "Urban Access"). Optional; when blank, rendering falls back to the full name.
• New Project.get_display_short_name() centralizes that fallback (display_short_name or name).
• Compact chips (display_pub_snippet, display_talk_snippet, display_video_snippet) now render get_display_short_name. The aria-label keeps the full name for screen readers; the link still uses the short_name slug.
• Admin help text clarified on all three name fields so editors can tell them apart:
  • name — full title shown as the heading
  • display_short_name — optional short card label (blank = use full name)
  • short_name — lowercase/no-spaces URL slug, not shown to readers
• display_short_name added to the Project admin form.

Bonus: slug-uniqueness guard

While here, added Project.clean() rejecting a short_name that collides case-insensitively with an existing project. The project view resolves /projects/<slug>/ via short_name__iexact, so a duplicate slug raises MultipleObjectsReturned — a 500 on both project pages. This is the form-level guard (mirrors the keyword-dedup approach); a DB-level unique constraint is deferred until prod data is confirmed de-duped (follow-up issue).

Before / After

Same publication card; the "before" state is reproduced by leaving display_short_name blank (the fallback path).

Testing

• python manage.py test website --settings=makeabilitylab.settings_test → 493 passed, 8 skipped.
• New tests in test_project.py: get_display_short_name fallback (set / None / empty) and slug-uniqueness validation (case-insensitive, self-excluded on edit).
• Verified on localhost: pub/talk/video chips render the short label, link uses the slug, aria-label keeps the full name; fallback confirmed on a project with no short name.

Notes

• No migration committed (migrations are gitignored / per-environment); the field is nullable and the entrypoint generates the delta on container start.

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