fix(data-export): name index.php in S3 completion redirects

[rumblefrog]

Description

Fixes the S3-delivery mode of the owner-only Full data export: pasting a presigned S3 URL and submitting produced a bare "POST required." screen instead of a success/error toast.

web/export.php's two completion redirects (sbpp_export_redirect_success / sbpp_export_redirect_failure) emitted a query-only Location: ?p=admin&c=export&result=... reference. Because the redirect fires from export.php, the browser resolved the empty-path reference against export.php's own path (RFC 3986 §5.2 keeps the base path) and followed it as a GET to export.php?p=admin&c=export..., landing straight in the POST-only method gate at the top of the script. The S3 upload had already run by then, so the operator saw a bogus error after a successful export.

Both arms now name the router entry point explicitly (Location: index.php?p=admin&c=export...), so the redirect resolves to /index.php?p=admin&c=export... and the admin page handler paints the toast.

ZIP mode streams its body to php://output and never redirects, which is exactly why only the S3 path was affected (ZIP downloads worked fine).

Motivation and Context

Operator report: "When I paste a presigned S3 URL into the export, I get a screen 'POST required.'"

The S3 completion path is the one export branch that redirects, and it had no end-to-end coverage (only the uploader class is unit-tested via transport injection), so the bad redirect target slipped through.

How Has This Been Tested?

• php -l clean on both edited files.
• Verified the new test's three assertions pass against the edited export.php:
  • no bare Location: ?p= remains,
  • success arm names index.php,
  • error arm names index.php.
• Confirmed these are the only two Location: redirects in export.php and that every S3 branch (success + all failure arms) routes through the two fixed helpers.

Added testEntryPointRedirectsNameIndexPhpNotBareQuery() to AdminExportPermissionTest.php as a regression guard (static-shape, no DB): fails if a bare Location: ?p= reappears.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.

_{Docs note: this is a redirect-path bugfix that makes the already-documented S3 flow work as written (no change to wire format, delivery modes, or the security model), so data-export.mdx / ARCHITECTURE.md need no update.}

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