When a document has no title, authors, date, or abstract, the article()
template unconditionally emitted a place(top, float: true, ...) with an
empty block. This counted as content, so a subsequent raw #set page(...)
in the document body triggered a page break in Typst, producing a blank
first page.

Guard the place() call so it is only emitted when there is actual title
block content.

Fixes #14217

When no pdf-standard is set in document YAML, fall back to the
QUARTO_PDF_STANDARD environment variable (comma-separated, e.g.
"ua-1" or "a-2b,ua-1"). This applies to LaTeX, Typst, and PDF
format resolution.

Includes a smoke test that verifies the env var produces the
expected \DocumentMetadata in LaTeX output.