COMPUTE-1649 Suggest shared GH Copilot instructions file; add initial anti-hallucination instructions (#522)

Author: r-i-v-a

.github/copilot-instructions.md

@@ -0,0 +1,8 @@
+# GitHub Copilot Instructions
+
+## Anti-Hallucination Guidelines
+
+- Always check actual file contents before making claims about code
+- When uncertain about implementation details, suggest investigation commands
+- Distinguish between speculation and verified facts
+- Reference specific line numbers when quoting code