docs(strong): record age-key issuance and the 3 bootstrap.sh bugs found fixing it

strong now has its own age key (issued over LAN via --no-mesh),
pubkey recorded in inventory.yaml. Not yet granted to any secrets
file - that's a separate decision.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

inventory.yaml

@@ -394,6 +394,7 @@ hosts:
       (filename kept as-is, it's a historical planning doc). Only Phase 1
       (Proxmox install + cluster join) is done; no physical
       drive move, service migration, or GPU passthrough has happened yet.
+    age_pubkey: age1rtwvdct6avjkr3cyxv3vue3vqx4d524fjfr3vk7xrnvyrylnry5sm54sn4
   netbird-vps:
     kind: external
     os: linux