revise topics/decision trees for decision tables terminology shift

[sei-renae]

This pull request updates the documentation for decision trees to clarify terminology and improve explanations, especially distinguishing between machine learning and operations-research meanings. It also enhances formatting and improves a reference link in the document.

Terminology clarification and context:

• Added an inline note at the top explaining that SSVC uses "decision tree" in the operations-research sense (hand-crafted choices), not the machine learning sense (statistically learned models), and notes the terminology shift to "decision table" in SSVC v2025.9 to reduce confusion. Includes a link to ADR-0014 for further details.

Documentation and formatting improvements:

• Applied markdownlint
• Updated references to external resources, such as the VRDA framework and the R data.tree package, to use direct links and clearer descriptions.

Markdownlint is unhappy about a few things:

decision_trees.md:56 error MD040/fenced-code-language Fenced code blocks should have a language specified [Context: "```"]
decision_trees.md:56 error MD046/code-block-style Code block style [Expected: indented; Actual: fenced]
decision_trees.md:77 error MD040/fenced-code-language Fenced code blocks should have a language specified [Context: "```"]
decision_trees.md:77 error MD046/code-block-style Code block style [Expected: indented; Actual: fenced]
decision_trees.md:92:2 error MD059/descriptive-link-text Link text should be descriptive [Context: "[here]"]

Resolves #990

[Copilot]

Pull request overview

This PR updates the “Decision Trees” topic documentation to clarify SSVC’s use of “decision tree” (operations-research meaning) vs. the machine-learning meaning, and to note the SSVC v2025.9 terminology shift toward “decision table” to reduce confusion.

Changes:

• Adds an inline note explaining SSVC’s terminology and linking to the relevant ADR.
• Refreshes/clarifies external references (e.g., VRDA, data.tree) and reflows text for readability.
• Minor documentation formatting updates in the examples and surrounding prose.

[sei-renae]

Resolves #991

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.