add AGENTS.md

Add AGENTS.md (.github/copilot-instructions.md references it via
@../AGENTS.md, symlink doesn't work due local links deferencing) to
allow AI assistants to be more effective, especially the Code Review
Bot.

Signed-off-by: Tuomo Tanskanen <[email protected]>

Author: tuminoid

.github/copilot-instructions.md

@@ -0,0 +1 @@
+@../AGENTS.md

.gitignore

@@ -74,3 +74,6 @@ go.work.sum
 
 # e2e result junit xml files
 junit.e2e_suite.*.xml
+
+# ai stuff
+.claude