AGENTS.md: record delete_branch_on_merge + disabled Wiki/Projects settings

[Laaaaksh]

Summary

Lands the AGENTS.md memory update from iteration 66 so future agents (and humans auditing settings) don't misdiagnose two intentional repo-settings choices:

• delete_branch_on_merge is on: after any PR merges — including this run's own gnhf branch PRs — GitHub deletes that head branch from origin. The note says to re-push the local branch to recreate it and not to misread the vanished origin ref as data loss.
• Wiki/Projects tabs are deliberately disabled: recorded so a future settings audit doesn't "fix" them back on.

Both facts were established in iteration 66 by verified API PATCH + re-read; this commit only records them in project memory. No code changes.

Verification

• gofmt -l . clean
• go build ./... pass
• go vet ./... pass
• go test ./... -race -count=1 green across all six packages