docs(reference): import Dune: Awakening server-manager references

Phase 2 references for the host-agent Dune adapter, moved out of volatile /tmp
into docs/reference-repos/ (per Commander). Three upstream projects, .git +
node_modules + compiled binaries stripped (16MB source). Nested AI-instruction
files (.claude/, CLAUDE.md) removed so they don't pollute Corrosion sessions.

- icehunter/    dune-admin (Go+React) — 4 control planes; SETUP_DOCKER.md is the
                closest analog to our agent's Dune docker control plane (compose
                lifecycle, docker logs, RabbitMQ-via-exec, dune Postgres schema)
- adainrivers/  Rust/Tauri desktop — SSH+k8s BattleGroup control, maintenance
                daemon, in-game admin console (Rust idiom reference)
- the4rchangel/ Node web UI replacing battlegroup.bat — matches the Commander's
                Hyper-V self-host path + game-config schema

See docs/reference-repos/README.md for the full index + how we use each.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/reference-repos/icehunter/cmd/dune-admin/presence.go

@@ -0,0 +1,47 @@
+package main
+
+// presenceTracker detects player join events by diffing the set of online
+// accounts across successive observations. The first observation seeds a silent
+// baseline so a dune-admin (re)start does not re-fire on-join actions (e.g. the
+// MOTD) for everyone already in-game; a player who goes offline and returns is a
+// new join. Keyed on account id (always present), which is also what the whisper
+// path consumes.
+//
+// Not safe for concurrent use: the scanner calls observe() serially from its
+// single goroutine.
+type presenceTracker struct {
+	seen   map[int64]struct{}
+	seeded bool
+}
+
+func newPresenceTracker() *presenceTracker {
+	return &presenceTracker{seen: map[int64]struct{}{}}
+}
+
+// observe records the currently-online accounts and returns those newly online
+// since the previous observation (join events). The first call returns no joins
+// (it only seeds the baseline).
+func (p *presenceTracker) observe(online []welcomeAccount) []welcomeAccount {
+	current := make(map[int64]struct{}, len(online))
+	var joins []welcomeAccount
+	for _, acc := range online {
+		current[acc.AccountID] = struct{}{}
+		if !p.seeded {
+			continue
+		}
+		if _, ok := p.seen[acc.AccountID]; !ok {
+			joins = append(joins, acc)
+		}
+	}
+	p.seen = current
+	p.seeded = true
+	return joins
+}
+
+// reset re-arms the baseline so the next observe is silent. Used when the MOTD
+// feature is toggled off (and later on) so currently-online players are not
+// messaged on the flip — only genuine future joins are.
+func (p *presenceTracker) reset() {
+	p.seen = map[int64]struct{}{}
+	p.seeded = false
+}