[ShivanshhhG]

Aligns the Terms and definitions chapter with ISO/IEC Directives Part 2 (Clause 16.5) drafting principles:

• Applied the principle of substitutability so definitions can replace the term directly in context.
• Removed leading articles ("a", "an", "the", "any") from definitions.
• Removed trailing full stops from single-sentence definitions.
• Moved descriptive and contextual notes into standard Note 1 to entry: blocks.
• Formatted source attributions into standard [SOURCE: ...] citations indicating modifications where applicable.

Closes #1504.

[bact]

Thank you for the cleanup. Should we keep the links to the source?

[ShivanshhhG]

Good call! Restored the links directly into the [SOURCE: ...] citations and the SEVOCAB note.