docs: fleet security plan v1.3 + tailnet ACL baseline

Phase 0 findings: password auth confirmed on (straylight, dixie), ACL
default allow-all, funnel-for-all, titan stale public funnel, gitea
public edge on nginx 1.18.0. Plan: 6 pillars, 6 phases, decisions and
assumptions register inline.

docs/tailscale-acl.hujson

@@ -0,0 +1,28 @@
+// Baseline tailnet policy, exported from Tailscale admin console 2026-11-01
+// by Kyle. Unmodified default policy — allow-all ACL, funnel enabled for all
+// members, default Tailscale SSH rule. Phase 2 of docs/security-plan.md
+// replaces this; keep as the pre-segmentation baseline.
+{
+	"acls": [
+		// Allow all connections.
+		{"action": "accept", "src": ["*"], "dst": ["*:*"]},
+	],
+
+	// Default Tailscale SSH: every member may SSH to their own devices,
+	// as nonroot or root.
+	"ssh": [
+		{
+			"action": "accept",
+			"src":    ["autogroup:members"],
+			"dst":    ["autogroup:self"],
+			"users":  ["autogroup:nonroot", "root"],
+		},
+	],
+	"nodeAttrs": [
+		{
+			// Any tailnet member can open a public Funnel endpoint.
+			"target": ["autogroup:members"],
+			"attr":   ["funnel"],
+		},
+	],
+}