docs: remove horizontal rules to follow own guidelines

Remove all --- section separators to comply with Universal Formatting
Rules. The ## headers provide sufficient visual separation.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/_STYLE_GUIDE.md

@@ -215,8 +215,6 @@ your-project/
 ```
 ````
 
----
-
 ## Document Types
 
 Select document type based on reader goal:
@@ -229,8 +227,6 @@ Select document type based on reader goal:
 | Look up information | Reference |
 | Find term definitions | Glossary |
 
----
-
 ## Tutorial Structure
 
 Tutorials teach complete workflows to new users. Length: 200-400 lines.
@@ -266,8 +262,6 @@ Tutorials teach complete workflows to new users. Length: 200-400 lines.
 - [ ] Getting Help section present
 - [ ] Key Takeaways admonition at end
 
----
-
 ## How-To Structure
 
 How-to guides complete specific tasks for users who know basics. Length: 50-150 lines (shorter than tutorials, assumes prior knowledge).
@@ -307,8 +301,6 @@ Guidelines:
 - [ ] Steps are numbered `###` subsections with action verbs
 - [ ] "What You Get" describes output artifacts
 
----
-
 ## Explanation Structure
 
 Explanation documents answer "What is X?" and "Why does X matter?"
@@ -396,8 +388,6 @@ Explanation documents answer "What is X?" and "Why does X matter?"
 - [ ] Links to how-to guides for procedural questions
 - [ ] 2-3 admonitions max per document (1-2 per section)
 
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-
 ## Reference Structure
 
 Reference documents answer "What are the options?" and "What does X do?" for users who know what they need.
@@ -486,8 +476,6 @@ Guidelines:
 - [ ] Links to explanation docs for conceptual depth
 - [ ] 1-2 admonitions max
 
----
-
 ## Glossary Structure
 
 Glossaries provide compact, scannable term definitions.
@@ -559,8 +547,6 @@ Reference category anchor (terms are not headers):
 - [ ] Term names bolded in cells
 - [ ] No "A [term] is..." definitions
 
----
-
 ## FAQ Sections
 
 Structure:
@@ -588,8 +574,6 @@ Rules:
 - Direct answers (no `**A:**` prefix)
 - End with CTA for unanswered questions
 
----
-
 ## Validation Steps
 
 Before submitting documentation changes, run from repo root: