feat: guest passage — slip through as a wanderer

POST /auth/guest mints a real user row (wanderer-<4 hex>, collision
retry, unusable random password) and issues the normal session cookie,
per-IP rate limited at 5/hour. EnterPage gains the guest action;
the séance shows a dismissible claim-a-name note for wanderer- users.

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

frontend/src/i18n/en.json

@@ -79,7 +79,8 @@
     "switchToRegister": "no name in the registry? first contact →",
     "switchToLogin": "already carved your name? reconnect →",
     "failed": "the veil rejected you: {{message}}",
-    "smallPrint": "your medium handle is only ever stored on this server"
+    "smallPrint": "your medium handle is only ever stored on this server",
+    "guest": "slip through as a wanderer"
   },
   "seance": {
     "modes": {
@@ -272,6 +273,11 @@
         "entity": "entity",
         "jitter": "jitter"
       }
+    },
+    "wanderer": {
+      "note": "your contacts fade with the mist —",
+      "claim": "claim a name to keep your codex",
+      "dismiss": "let the mist take it"
     }
   },
   "codex": {

frontend/src/i18n/es.json

@@ -79,7 +79,8 @@
     "switchToRegister": "¿sin nombre en el registro? primer contacto →",
     "switchToLogin": "¿ya grabaste tu nombre? reconectar →",
     "failed": "el velo te rechazó: {{message}}",
-    "smallPrint": "tu nombre de médium solo se guarda en este servidor"
+    "smallPrint": "tu nombre de médium solo se guarda en este servidor",
+    "guest": "escabúllete como errante"
   },
   "seance": {
     "modes": {
@@ -272,6 +273,11 @@
         "entity": "entidad",
         "jitter": "fluctuación"
       }
+    },
+    "wanderer": {
+      "note": "tus contactos se desvanecen con la niebla —",
+      "claim": "reclama un nombre para conservar tu códice",
+      "dismiss": "deja que la niebla se lo lleve"
     }
   },
   "codex": {