Use request host for exhibit URLs instead of hardcoded jandig.app (#822)

[vjpixel]

Summary

Exhibit detail and create-exhibit pages were rendering URL previews and "share" links with a hardcoded https://jandig.app/. On dev, an exhibit at dev.jandig.app/exhibit/?id=N showed a share URL pointing at https://jandig.app/<slug>/, sending users away from the dev environment they were testing on.

Switch user-facing references to {{ request.scheme }}://{{ request.get_host() }}/ so each environment links to itself. The "See this exhibition" anchor in exhibit_detail.jinja2 uses a relative /{slug} path, which avoids the question entirely.

Files changed

• src/core/jinja2/core/exhibit_detail.jinja2:
  • Display URL → {{ request.scheme }}://{{ request.get_host() }}/<slug>
  • Anchor href → /{slug} (relative)
• src/core/jinja2/core/exhibit_create_ar.jinja2 / exhibit_create_mr.jinja2:
  • URL-helper preview label → dynamic host

Test plan

• On dev.jandig.app/exhibit/?id=…: share link reads dev.jandig.app/<slug> and clicking goes to dev.jandig.app/<slug> (not production).
• On jandig.app/exhibit/?id=…: share link reads jandig.app/<slug> (unchanged behaviour).
• Create-exhibit "Your exhibit URL will look like this" preview uses the current host.

Closes #822

https://claude.ai/code/session_01XC1THLWgnGXGf5wgRhdyvB

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Generated by Claude Code

[pablodiegoss]

We probably can use request.host here, but not request.scheme. I've not confirmed it, but SSL termination happens on our elastic load balancer on Amazon, using request.scheme here is probably going to return "http:" and http links are always redirected to https, so this will make all users be redirected once on each link.

We should keep https:// hardcoded to avoid any issues with internal network schemes, and use only the host part to get "dev.jandig.app" or "jandig.app" here