Style guide update

[giorgionaps]

Description

Closes #7785. Style guide updates. Updates to match what's been added to confluence earlier:

• Added UI text to the style guide application scope
• Aligned admonitions with Confluence rules (limited types + explicit avoid list)
• Made section linking mandatory and aligned link behavior (deep links, /docs routing, new-tab external links, UI exception)
• Added AP Style guidance for quotation marks
• Clarified time zones and daylight savings, including range formatting
• Updated titles and headers to require action-oriented wording and added the blog title casing exception
• Added retroactive step reference rule to numerical lists
• Added guidance for CLI commands and details elements
• Added job title capitalization exceptions, including leadership lists

New additions:

• Sub-section linking: in Grammar > Bolding and Implementation steps > Links, explicitly clarified that section references must be descriptive links rather than bold text.
• Contractions: added a new row in Grammar > Contractions explicitly encouraging the use of common contractions for a natural, conversational tone.
• Empowering language: in Grammar > Empowering language, specified using framing like "With , you’ll..." to focus on user outcomes.
• Sub-process usage: in Product names and other terminology > BPMN sub-process terminology, clarified the requirement to use the hyphenated "sub-process" in user-facing prose.

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support. (add bug or support label)
• This is already available but undocumented and should be released within a week. (add available & undocumented label)
• This is on a specific schedule and the assignee will coordinate a release with the Documentation team. (create draft PR and/or add hold label)
• This is part of a scheduled alpha or minor. (add alpha or minor label)
• There is no urgency with this change (add low prio label)

PR Checklist

• The commit history of this PR is cleaned up, using {type}(scope): {description} commit message(s)

• My changes are for an upcoming minor release and are in the /docs directory (version 8.9).
• My changes are for an already released minor and are in a /versioned_docs directory.

• I added a DRI, team, or delegate as a reviewer for technical accuracy and grammar/style:
  • Engineering team review
  • Technical writer review via @camunda/tech-writers unless working with an embedded writer.

[christinaausley]

Semi-relates to #7465 (for my tracking purposes 😄)

[christinaausley]

Thank you! 🥳