✨ Adds documentation instructions for ADR, analyzers, and observability

Introduces new markdown files detailing editing rules for ADRs,
guidelines for analyzer and style configuration, and best practices
for observability and feature flags. These documents aim to ensure
consistency and clarity in project documentation and code quality.

Co-authored-by: Copilot <copilot@github.com>

.github/instructions/documentation.instructions.md

@@ -0,0 +1,47 @@
+---
+description: "README.md authoring: structure, callouts, diagrams, and assets."
+applyTo: "**/README.md"
+---
+# README Style
+
+## Structure
+
+Follow this ordering when sections apply; omit those that don't:
+
+1. **Title** (`# <ProjectName>`) and one-sentence purpose.
+1. **Getting Started** — minimal commands to consume or run the project.
+1. **Features** / **Capabilities** — bulleted highlights.
+1. **Configuration** — build args, environment variables, MSBuild properties.
+1. **Usage Examples** — code or CLI snippets.
+1. **Recommendations** / **Caveats** — known limitations, in callouts.
+1. **Reference link definitions** at the bottom.
+
+## Conventions
+
+- Do not hard-wrap prose; one paragraph per line.
+- Ordered lists: write every item as `1.` and let the renderer auto-number.
+- Use reference-style links for external URLs in prose, with definitions at the bottom of the file. Inline links are fine in tables and for in-repo relative paths.
+- Keep code examples minimal — strip boilerplate unless it is the point.
+
+## Callouts
+
+Use [GitHub-flavoured alerts](https://docs.github.com/en/get-started/writing-on-github/getting-started-with-writing-and-formatting-on-github/basic-writing-and-formatting-syntax#alerts) for emphasis; reserve plain `>` blockquotes for quoted text.
+
+| Alert | Use for |
+| --- | --- |
+| `> [!NOTE]` | Neutral context the reader should know |
+| `> [!TIP]` | Optional best-practice |
+| `> [!IMPORTANT]` | Required for correct usage |
+| `> [!WARNING]` | Risk of breakage or data loss |
+| `> [!CAUTION]` | Security or destructive-action risk |
+
+## Mermaid Diagrams
+
+- Match diagram type to intent: `flowchart` (processes), `sequenceDiagram` (interactions over time), `classDiagram` (type relationships), `erDiagram` (data models).
+- Keep diagrams under ~15 nodes; split larger ones.
+- No custom styling — defaults render in both light and dark modes.
+
+## Assets
+
+- Repo-wide assets in `/docs/assets/`; project-scoped assets in the project's own `docs/assets/`.
+- Prefer **SVG** for diagrams and logos; PNG only for raster screenshots.