docs(agents): retire the six role briefs under .github/instructions/

.changeset/retire-role-briefs.md

@@ -0,0 +1,7 @@
+---
+---
+
+Agent instructions only — this PR releases nothing to HotCRM users, so the frontmatter
+above is deliberately empty. The six per-role briefs under `.github/instructions/` are
+retired and `AGENTS.md` is the one instruction set; no file under `src/`, no config and
+no published artifact changes.

.github/AGENT_GUIDE.md

@@ -2,7 +2,7 @@
 
 The following directories contain the "Brain" of the HotCRM development process.
 
-- `instructions/`: **Role-Based Handbooks**. Define HOW to write code for specific domains (Metadata, Logic, UI).
+- `/AGENTS.md`: **The one instruction set**. Defines HOW to write code in this repo; there are no per-role handbooks.
 - `tasks/`: **Prompt Templates**. Ready-to-use prompts to copy-paste into your AI chat window.
 - `copilot-instructions.md`: **System Prompt**. The meta-instructions for GitHub Copilot.
 
@@ -11,4 +11,4 @@ The following directories contain the "Brain" of the HotCRM development process.
 1.  **Define**: Create an Issue using `ISSUE_TEMPLATE/ai_task.yml`.
 2.  **Prompt**: Copy a template from `tasks/` and fill it with details from the Issue.
 3.  **Execute**: Paste into Copilot/Cursor/Windsurf.
-4.  **Review**: Verify against the standards in `instructions/`.
+4.  **Review**: Verify against the standards in `/AGENTS.md`.