Support Persian and RTL document generation

[tghosth]

Summary

• install the bilingual Amiri font in the document builder
• provide the LaTeX fallback needed for Persian zero-width non-joiners
• right-align default/left table columns in RTL PDF and TeX output
• leave LTR documents unchanged when direction metadata is absent

Scope

This PR contains only reusable document-generation changes extracted from #3370. It excludes Persian translation content, generated outputs, and changes to 5.0/languages.txt.

Validation

• git diff --check passes
• the RTL filter was used to generate and visually inspect Persian requirement-table pages
• the filter includes a guard for LTR documents without dir metadata