feat(isn): VLAN-4 routed sub-interface + addr on spine ISN ospfIf; ISN-CSW LLDP neighbor (v0.19.0)

Real ACI multi-site spines carry the OSPF address toward the ISN on a
routed sub-interface, not the bare port: ospfIf id/dn are now
eth1/{49+si}.4 with addr=172.16.{site}.{si+1}/24 (same /24 as the
existing .254 peer); ospfAdjEp nests under the sub-if. Each spine ISN
uplink physical port also gets an ISN-CSW lldpAdjEp/cdpAdjEp
(sysName ISN-CSW{site}, portIdV Ethernet1/{si+1}, model N9K-C9364C,
locally-administered 02:1B:0D MAC hashed from site.id). Single-site
fabrics build none of this. Closes the autoACI Fabric (physical) gap
where spine uplink rows showed blank Local IP / Neighbor Port.
908 tests green.

README.md

@@ -415,7 +415,9 @@ $ aci-sim show --json | jq '.sites[0].nodes[0]'
 Builds the topology fresh (same builders the sim boots with) and prints a
 **`show lldp neighbors`-style table** of every `lldpAdjEp` adjacency —
 i.e. the neighbor relationships the cabling in `topology.yaml` implies
-(spine<->leaf links, APIC<->leaf attachment), materialized exactly the way
+(spine<->leaf links, APIC<->leaf attachment, plus — multi-site only — each
+spine's ISN uplink toward the inter-site switch, `ISN-CSW{site}`),
+materialized exactly the way
 they'd appear on a running sim (§10's LLDP/CDP fidelity). Pass `--cdp` to
 read `cdpAdjEp` instead. This does not start any server — it's a static,
 read-only view of one freshly-built site (or all sites).