Replace 'must' with 'shall' in sources directory

[Copilot]

This PR systematically replaces all occurrences of the term 'must' with 'shall' in the sources directory and subdirectories as requested.

Changes Made

• 04-spec.adoc: Updated 8 validation rules in the "Validation rules for reference paths" section
• 05-validation.adoc: Updated 16 validation rules across entity mapping, attribute mapping, reference path validation, and overall consistency sections

All changes maintain the same semantic meaning while using the more formal "shall" terminology, which is standard in technical specifications and requirements documentation.

Files Modified

• sources/sections/04-spec.adoc (8 replacements)
• sources/sections/05-validation.adoc (16 replacements)
• .gitignore (added build artifacts exclusions)

Verification

• ✅ All 24 occurrences of 'must' successfully replaced with 'shall'
• ✅ AsciiDoc syntax validation passed
• ✅ Documentation builds successfully with Metanorma
• ✅ No remaining 'must' occurrences in sources directory
• ✅ Generated HTML output confirmed the replacements

The changes are purely textual replacements that improve the formal tone of the specification without altering any functional requirements or technical content.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• archive.ubuntulinux.jp
  • Triggering command: ruby /usr/local/bundle/bin/metanorma sources/document.adoc --agree-to-terms (dns block)
• distrib-coffee.ipsl.jussieu.fr
  • Triggering command: ruby /usr/local/bundle/bin/metanorma sources/document.adoc --agree-to-terms (dns block)
• ftp.jaist.ac.jp
  • Triggering command: ruby /usr/local/bundle/bin/metanorma sources/document.adoc --agree-to-terms (dns block)
• ftp.klid.dk
  • Triggering command: ruby /usr/local/bundle/bin/metanorma sources/document.adoc --agree-to-terms (dns block)
• ftp.sjtu.edu.cn
  • Triggering command: ruby /usr/local/bundle/bin/metanorma sources/document.adoc --agree-to-terms (dns block)
• mirror.math.princeton.edu
  • Triggering command: ruby /usr/local/bundle/bin/metanorma sources/document.adoc --agree-to-terms (dns block)
• mirrors.uni-ruse.bg
  • Triggering command: ruby /usr/local/bundle/bin/metanorma sources/document.adoc --agree-to-terms (dns block)
• openvz.mirror.garr.it
  • Triggering command: ruby /usr/local/bundle/bin/metanorma sources/document.adoc --agree-to-terms (dns block)
• web.archive.org
  • Triggering command: ruby /usr/local/bundle/bin/metanorma sources/document.adoc --agree-to-terms (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

---

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[TRThurman]

@ronaldtse Please review this PR for document version update requirement

[ronaldtse]

Thank you @TRThurman !