docs(references): port style guides, 24 diagram guides, and 9 templates from opencode

All content ported from borealBytes/opencode under Apache-2.0 license with
attribution headers prepended to each file.

- references/markdown_style_guide.md (~733 lines): full markdown formatting,
  citation, collapsible sections, emoji, Mermaid integration, and template
  selection guide
- references/mermaid_style_guide.md (~458 lines): full Mermaid standards —
  emoji set, classDef color palette, accessibility (accTitle/accDescr),
  theme neutrality (no %%{init}), and diagram type selection table
- references/diagrams/ (24 files): per-type exemplars, tips, and templates
  for all Mermaid diagram types
- templates/ (9 files): PR, issue, kanban, ADR, presentation, how-to,
  status report, research paper, project docs

Source: https://github.com/borealBytes/opencode

scientific-skills/markdown-mermaid-writing/references/diagrams/pie.md

@@ -0,0 +1,52 @@
+<!-- Source: https://github.com/borealBytes/opencode | License: Apache-2.0 | Author: Clayton Young / Superior Byte Works, LLC (Boreal Bytes) -->
+
+# Pie Chart
+
+> **Back to [Style Guide](../mermaid_style_guide.md)** — Read the style guide first for emoji, color, and accessibility rules.
+
+**Syntax keyword:** `pie`
+**Best for:** Simple proportional breakdowns, budget allocation, composition, survey results
+**When NOT to use:** Trends over time (use [XY Chart](xy_chart.md)), exact comparisons (use a table), more than 7 categories
+
+---
+
+## Exemplar Diagram
+
+```mermaid
+pie
+    accTitle: Engineering Time Allocation
+    accDescr: Pie chart showing how engineering team time is distributed across feature work, tech debt, bug fixes, on-call, and learning
+
+    title 📊 Engineering Time Allocation
+    "🔧 Feature development" : 45
+    "🔄 Tech debt reduction" : 20
+    "🐛 Bug fixes" : 20
+    "📱 On-call & support" : 10
+    "📚 Learning & growth" : 5
+```
+
+---
+
+## Tips
+
+- Values are proportional — they don't need to sum to 100
+- Use descriptive labels with **emoji prefix** for visual distinction
+- Limit to **7 slices maximum** — group small ones into "📦 Other"
+- Always include a `title` with relevant emoji
+- Order slices largest to smallest for readability
+
+---
+
+## Template
+
+```mermaid
+pie
+    accTitle: Your Title Here
+    accDescr: Describe what proportions are being shown
+
+    title 📊 Your Chart Title
+    "📋 Category A" : 40
+    "🔧 Category B" : 30
+    "📦 Category C" : 20
+    "🗂️ Other" : 10
+```