feat: share credentials with users and roles, inherit data on account deletion (#1342)

* feat: share credentials with users and roles, inherit data on account deletion

Credentials can be shared at "use" or "manage" level. Recipients get
a copy re-encrypted under their own data key (shared_credential_secrets),
kept in step with the owner's row through the same lifecycle hooks as
shared host secrets. One gate, findUsableCredential(), replaces the
private-namespace lookups so a shared credential works wherever a
private one does. Deleting a user now hands their hosts and credentials
to a successor (the deleting admin by default) instead of revoking
everything they shared.

* fix: harden credential ownership transfer

drizzle/mysql/meta/_journal.json

@@ -127,6 +127,13 @@
       "when": 1787596414390,
       "tag": "0017_spicy_proteus",
       "breakpoints": true
+    },
+    {
+      "idx": 18,
+      "version": "5",
+      "when": 1787600445146,
+      "tag": "0018_fancy_barracuda",
+      "breakpoints": true
     }
   ]
 }