feat: fullscreen toggle for cooking assistant and recipe chat

Both chat panels were locked to a fixed 420px slide-over with no way
to get more room for longer conversations. Adds an expand/collapse
button in the header that grows the sheet to fill the viewport.

v0.38.0

apps/web/messages/en.json

@@ -530,6 +530,8 @@
     "noRecent": "No public recipes yet."
   },
   "common": {
+    "expand": "Expand to fullscreen",
+    "collapse": "Exit fullscreen",
     "loading": "Loading…",
     "error": "Something went wrong",
     "save": "Save",

apps/web/messages/fr.json

@@ -530,6 +530,8 @@
     "noRecent": "Aucune recette publique pour l'instant."
   },
   "common": {
+    "expand": "Passer en plein écran",
+    "collapse": "Quitter le plein écran",
     "loading": "Chargement…",
     "error": "Une erreur s'est produite",
     "save": "Enregistrer",