fix: use object key for partial ID to match template reference

loadTemplates with an array registers the partial using the full file
path as its Handlebars ID (e.g.
'systems/fvtt-lethal-fantasy/templates/chat/_dice-breakdown.hbs'), but
the template references it by the short name 'chat/dice-breakdown'.
Using an object with explicit keys ensures the partial ID matches.

join-page.txt

@@ -0,0 +1,25 @@
+uid=12_0 RootWebArea "Lethal Fantasy" url="https://localhost:31000/join"
+  uid=12_1 banner
+    uid=12_2 heading "Lethal Fantasy" level="1"
+  uid=12_3 form
+    uid=12_4 heading "Rejoindre la partie" level="2"
+    uid=12_5 combobox expandable haspopup="menu"
+      uid=12_6 option selectable selected
+      uid=12_7 option "Player2" selectable value="Player2"
+    uid=12_8 textbox "Mot de passe"
+    uid=12_9 contentinfo
+      uid=12_10 button "REJOINDRE LA PARTIE"
+  uid=12_11 heading "Détails de la session" level="2"
+  uid=12_12 StaticText " Prochaine partie"
+  uid=12_13 StaticText " Joueurs présents"
+  uid=12_14 StaticText "1"
+  uid=12_15 StaticText "/"
+  uid=12_16 StaticText "2"
+  uid=12_17 form
+    uid=12_18 heading "Retour à l’accueil" level="2"
+    uid=12_19 textbox
+    uid=12_20 contentinfo
+      uid=12_21 button "RETOUR À L’ACCUEIL"
+  uid=12_22 heading "Description du monde" level="2"
+  uid=12_23 contentinfo
+    uid=12_24 StaticText "Version 14 Build 364"