feat(settings): a Pet page for the mascot

Settings -> Pet (/settings/pet, PetSettings.tsx): show/hide, speech
bubbles, size with a live preview, and the pet grid - Sagi, featured
codex-pets.net pets (downloaded on first pick), your own (deletable) -
with image upload and .codex-pet.zip import. The Sagi block leaves
General; the mascot menu's Pet settings opens the page. PetMenu and the
page share components/Sagi/usePets.ts.

client/src/i18n/locales/en/settings.json

@@ -22,7 +22,11 @@
       "browse": "Find more on codex-pets.net",
       "settings": "Pet settings…"
     },
-    "petHint": "Right-click the mascot to choose its pet — Sagi, a featured or imported Codex pet, or your own image — and its size."
+    "bubbles": "Speech bubbles",
+    "bubblesDesc": "Let the pet comment on your sessions in a bubble",
+    "sizeDesc": "{{min}}–{{max}} px; the preview is capped at 120 px",
+    "chooseDesc": "Featured pets come from codex-pets.net and are downloaded into this install the first time you pick one. Your choice and size are saved in this browser.",
+    "uploadHint": "An image (PNG, JPEG, GIF, WebP — no SVG) is shown still; a .codex-pet.zip (pet.json + a 1536×1872 spritesheet.webp) is animated by mood."
   },
   "pricing": {
     "vendor": {
@@ -676,6 +680,10 @@
         "title": "Appearance",
         "description": "Colour mode and theme. Saved in this browser only."
       },
+      "pet": {
+        "title": "Pet",
+        "description": "The corner mascot: show it, its size, speech bubbles, and which pet it wears."
+      },
       "notifications": {
         "title": "Notifications",
         "description": "Browser notifications, alert rules and webhooks."