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/quadrant.md

@@ -0,0 +1,66 @@
+<!-- Source: https://github.com/borealBytes/opencode | License: Apache-2.0 | Author: Clayton Young / Superior Byte Works, LLC (Boreal Bytes) -->
+
+# Quadrant Chart
+
+> **Back to [Style Guide](../mermaid_style_guide.md)** — Read the style guide first for emoji, color, and accessibility rules.
+
+**Syntax keyword:** `quadrantChart`
+**Best for:** Prioritization matrices, risk assessment, two-axis comparisons, effort/impact analysis
+**When NOT to use:** Time-based data (use [Gantt](gantt.md) or [XY Chart](xy_chart.md)), simple rankings (use a table)
+
+> ⚠️ **Accessibility:** Quadrant charts do **not** support `accTitle`/`accDescr`. Always place a descriptive _italic_ Markdown paragraph directly above the code block.
+
+---
+
+## Exemplar Diagram
+
+_Priority matrix plotting engineering initiatives by effort required versus business impact, helping teams decide what to build next:_
+
+```mermaid
+quadrantChart
+    title 🎯 Engineering Priority Matrix
+    x-axis Low Effort --> High Effort
+    y-axis Low Impact --> High Impact
+    quadrant-1 Do First
+    quadrant-2 Plan Carefully
+    quadrant-3 Reconsider
+    quadrant-4 Quick Wins
+    Upgrade auth library: [0.3, 0.9]
+    Migrate to new DB: [0.9, 0.8]
+    Fix typos in docs: [0.1, 0.2]
+    Add dark mode: [0.4, 0.6]
+    Rewrite legacy API: [0.95, 0.95]
+    Update CI cache: [0.15, 0.5]
+    Add unit tests: [0.5, 0.7]
+```
+
+---
+
+## Tips
+
+- Label axes with `Low X --> High X` format
+- Name all four quadrants with **actionable** labels
+- Plot items as `Name: [x, y]` with values 0.0–1.0
+- Limit to **5–10 items** — more becomes cluttered
+- Quadrant numbering: 1=top-right, 2=top-left, 3=bottom-left, 4=bottom-right
+- **Always** pair with a Markdown text description above for screen readers
+
+---
+
+## Template
+
+_Description of the two axes and what the quadrant placement means:_
+
+```mermaid
+quadrantChart
+    title 🎯 Your Matrix Title
+    x-axis Low X Axis --> High X Axis
+    y-axis Low Y Axis --> High Y Axis
+    quadrant-1 High Both
+    quadrant-2 High Y Only
+    quadrant-3 Low Both
+    quadrant-4 High X Only
+    Item A: [0.3, 0.8]
+    Item B: [0.7, 0.6]
+    Item C: [0.2, 0.3]
+```