fix: derive per-node IOL app id so linked routers get distinct MACs

IOL derives interface MACs from its application ID. With a constant
local-app every node shared the same MACs, and linked routers dropped
each other's frames as MAC loops — ARP never resolved and pings were
100% lost even though the whole uBridge datapath was forwarding.

Derive local-app from the node UUID (stable across restarts, kept in
1..1022) and align remote-app with the netiomux convention CML uses
(1023). Verified end to end: two iol-xe nodes, Ethernet0/0 link,
ARP resolves both ways, ping 4/5 (first loss = ARP), graceful
stop/start keeps the NVRAM config.

docs/features/iol-runner-docker.md

@@ -137,7 +137,10 @@ diagnosing wiring issues).
   `GNS3_IOL_MEMORY` (default 2048 MB). Keep container memory at IOL memory
   + ~512 MB headroom or the OOM-killer will shoot the router.
 * **MAC addresses**: the `mac_address` template field and per-adapter custom
-  MACs are ignored — IOL derives its own scheme (`aabb.cc00.0XY0`).
+  MACs are ignored — IOL derives its own scheme from the node's application
+  ID (`aabb.cc{app}{iface}`), e.g. `aabb.cc03.0400`. The ID is derived from
+  the node UUID so linked routers always get distinct MACs (nodes sharing an
+  ID would silently drop each other's frames as MAC loops).
 * **Interface names are IOL-style `Ethernet0/0`**, not `GigabitEthernet0/0`
   (4 ports per unit, matching the adapter-count granularity) — startup
   configs addressing `GigabitEthernet…` are rejected by the parser.