Add Copilot setting and conventions (#12807)

### What problem does this PR solve?

Added project instructions for setting up and running the application.

### Type of change

- [x] Documentation Update

.github/copilot-instructions.md

@@ -1 +1,22 @@
-Refer to [AGENTS.MD](../AGENTS.md) for all repo instructions.
+# Project instructions for Copilot
+
+## How to run (minimum)
+- Install:
+  - python -m venv .venv && source .venv/bin/activate
+  - pip install -r requirements.txt
+- Run:
+  - (fill) e.g. uvicorn app.main:app --reload
+- Verify:
+  - (fill) curl http://127.0.0.1:8000/health
+
+## Project layout (what matters)
+- app/: API entrypoints + routers
+- services/: business logic
+- configs/: config loading (.env)
+- docs/: documents
+- tests/: pytest
+
+## Conventions
+- Prefer small, incremental changes.
+- Add logging for new flows.
+- Add/adjust tests for behavior changes.