[pournasserian]

Closes #2629

What

Follow-ups from the independent review of #2601 (F-MED, #2427).

• Base version. The asset page's hidden BaseVersion comes from the form being shown. A form refused for its own problems keeps the version it started from, so its next save is refused as a conflict instead of overwriting a change saved meanwhile.
• Refused uploads no longer filter the library.
  • The return query uses upload-error, upload-folder, upload-tags, upload-alt and upload-caption, which no list filter reads.
  • A field whose escaped text is over 1500 characters isn't carried back. upload-dropped names it, and the form says to type it again, so the redirect stays well inside the server's request line limit.
  • Empty fields are left out of the return query.
• sub and uploaded are read as text. sub takes 1 or true. A value that isn't a flag counts as false instead of failing the page with a 500. uploaded has the same bug as sub, so it is fixed here too.
• Where-used rows link to the item's audit history. An entity type's items link as entity and other items as entry, as the log names them.
• An upload that declares a body over the limit gets the library's "too large" message instead of a reset connection.
  • UseMediaUploadLimit runs before the anti-forgery check. It reads and discards the declared body, then redirects back to the library.
  • It applies to a signed-in person, with a body up to 1 GB.
  • A chunked body that declares no length still meets the server's limit.

Why

• Discard the body, then answer. A browser still sending its upload treats an early answer as a failed request. Kestrel aborts a drain over the endpoint's limit, so the limit is lifted for that request only.
• Upload names of its own. The upload form and the list share the page, so names the list doesn't read can never filter it.

Tests

• The media screen tests run on SQLite and PostgreSQL.
• An anonymous upload goes to sign-in.
• The Keep the media details form's base version and stop refused uploads filtering the library #2629 overwrite scenario ends in the conflict message, and the other person's change stays.
• After a refused upload, the library lists every asset.
• A refused SVG upload says its type can't be uploaded.
• A PDF downloads as an attachment, with its file name.
• sub=1 lists subfolders, and sub=yes doesn't.
• uploaded=abc shows the page without the upload note.
• An upload declared over the limit comes back with the too-large message and stores nothing.
• Where-used rows link to an entry's history, and to an entity's history as entity, in bUnit.
• bUnit:
  • The upload's fields never filter the list.
  • A dropped field is named.
  • The sub flag takes 1 and true.
  • The return query drops a text too long to carry.

SignedInPageTests gives each page load a 30-second deadline that names the page. That test hung once on PostgreSQL in CI on v2, and passed on re-run, so the next failure says which page it was.

dotnet build -warnaserror, the unit and bUnit suite and the media tests on SQLite and PostgreSQL pass locally. No new package and no new project reference.

Checklist

• Linked to an issue a maintainer has confirmed
• Targets v2
• Tests or docs updated where behaviour changed
• No tool-generated co-author trailers or footers