Consolidate label rendering on per-vocab templates, retire $ldt:lang

[namedgraph]

Summary

Fixes duplicate bilingual widget headings (e.g. BacklinksBacklinks, Related resultsResultados relacionados) and makes the browser's ordered language preference govern label selection. Companion PR: AtomGraph/Web-Client#89 (requires client 5.0.3-SNAPSHOT).

• client.xsl imports the Web-Client per-vocab stylesheets (same order as internal-layout.xsl, so CSR label precedence = SSR by construction) and drops the monolithic ac:label/ac:description override, whose unfiltered fallback emitted every language variant when the browser language matched neither @en nor @es.
• $ac:langs is overridden client-side from navigator.languages (SaxonJS marshals it as an XDM sequence); server-side the Web-Client writer passes the request's Accept-Language. Label selection is no longer capped by the supportedLanguages config — a @lt label wins for an lt-preferring user while Content-Language still negotiates against en,es.
• Property-value suppression in bs2:PropertyList negotiates per property over $ac:langs (two split templates with cheap match patterns): the best accepted language wins; values in unaccepted languages stay hidden as before.
• sh.xsl label/description templates migrated; all xsl:sort collations use $ac:lang; dual use-when sort pairs collapsed.
• Client-side ac:uuid() override added (window.generateUUID), completing the removal of ixsl from Web-Client.
• $ldt:lang is fully retired from this repo (0 references); it remains the SSR Content-Language carrier in Web-Client.

Test plan

Verified in the browser against three preference configurations, all rendering single-language labels with SSR/CSR parity:

Accept-Language	UI chrome	Data labels
es,lt;q=0.9,en-US;q=0.8,en;q=0.7	Spanish (Registrarse, Resultados relacionados)	Lithuanian
lt,en-US;q=0.9,en;q=0.8	English	Lithuanian
en-US,en;q=0.9	English	English where available, first-available fallback otherwise

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