[BUGFIX] Render unpublished publications in citation styles #90

Unpublished publications currently render as TODO in the IEEE, APA and Vancouver-based citation styles. The default style already renders these records, but omits their note and publication language.

This change adds the missing unpublished output to Citestyle1 (IEEE), Citestyle4 (APA) and Citestyle9 (Vancouver-based), and includes language and note in Citestyle0. Citestyle6 inherits the IEEE output and continues to append the abstract. The existing author sections and link blocks are reused.

A supplied note is used as the publication status. If it is absent, IEEE and APA use the existing localized bibtype.unpublished label. The fallback does not assume that the work is a manuscript. APA renders an optional year, an
italic title and an available affiliation/institution. An absent year is omitted, matching the existing template behavior for other publication types; this does not claim complete APA handling of undated works.

For an unpublished record with author Uma Example, title A synthetic unpublished work, year 2025 and note Submitted for review, the output includes:

IEEE: U. Example, "A synthetic unpublished work", Submitted for review.
APA: Example, U. (2025). A synthetic unpublished work [Submitted for review].
Vancouver-based: Example U. A synthetic unpublished work. 2025. Submitted for review.

APA additionally outputs the institution when available. On a German page, the status falls back to nicht veröffentlicht (IEEE) or [Nicht veröffentlicht] (APA) if no note is supplied. The publication's own language marker is independent of the page language.

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