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/zenuml.md

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+<!-- Source: https://github.com/borealBytes/opencode | License: Apache-2.0 | Author: Clayton Young / Superior Byte Works, LLC (Boreal Bytes) -->
+
+# ZenUML Sequence Diagram
+
+> **Back to [Style Guide](../mermaid_style_guide.md)** — Read the style guide first for emoji, color, and accessibility rules.
+
+**Syntax keyword:** `zenuml`
+**Best for:** Code-like sequence diagrams, method-call-style interactions, developers familiar with programming syntax
+**When NOT to use:** Prefer standard [Sequence Diagrams](sequence.md) for most use cases — ZenUML requires an external plugin and has limited GitHub support.
+
+> ⚠️ **GitHub support:** ZenUML requires the `@mermaid-js/mermaid-zenuml` external module. It may **not render** on GitHub natively. Use standard `sequenceDiagram` syntax for GitHub compatibility.
+>
+> ⚠️ **Accessibility:** ZenUML does **not** support `accTitle`/`accDescr`. Always place a descriptive _italic_ Markdown paragraph directly above the code block.
+
+---
+
+## Exemplar Diagram
+
+_ZenUML sequence diagram showing a user authentication flow with credential validation and token generation using programming-style syntax:_
+
+```mermaid
+zenuml
+    @Actor User
+    @Boundary AuthAPI
+    @Entity Database
+
+    // User initiates login
+    User->AuthAPI.login(credentials) {
+        AuthAPI->Database.findUser(email) {
+            return user
+        }
+        if (user.valid) {
+            return token
+        } else {
+            return error
+        }
+    }
+```
+
+---
+
+## Tips
+
+- Uses **programming-style syntax** with method calls: `A->B.method(args)`
+- Curly braces `{}` create natural nesting (activation bars)
+- Control flow: `if/else`, `while`, `for`, `try/catch/finally`, `par`
+- Participant types: `@Actor`, `@Boundary`, `@Entity`, `@Database`, `@Control`
+- Comments with `//` render above messages
+- `return` keyword draws return arrows
+- **Prefer standard `sequenceDiagram`** for GitHub compatibility
+- Use ZenUML only when the code-style syntax is specifically desired
+
+---
+
+## Template
+
+_Description of the interaction flow:_
+
+```mermaid
+zenuml
+    @Actor User
+    @Boundary Server
+    @Entity DB
+
+    User->Server.request(data) {
+        Server->DB.query(params) {
+            return results
+        }
+        return response
+    }
+```