fix: show unlock hint on locked codex entries (#146)

Locked codex entries previously showed only '???' with no indication
of how to unlock them. Each entry now displays a hint generated from
its sourceType and sourceId (e.g. 'Defeat Troll King', 'Complete:
Shadow Mere').

Closes #146

apps/web/src/components/game/codexPanel.tsx

@@ -49,6 +49,40 @@ const sourceTypeFolder: Record<CodexEntry["sourceType"], string> = {
   zone:        "zones",
 };
 
+/**
+ * Converts a snake_case ID to a Title Case display name.
+ * @param id - The snake_case identifier to format.
+ * @returns The formatted display name.
+ */
+const formatId = (id: string): string => {
+  return id.split("_").
+    map((word) => {
+      return word.charAt(0).toUpperCase() + word.slice(1);
+    }).
+    join(" ");
+};
+
+/**
+ * Generates a human-readable unlock hint for a locked codex entry.
+ * @param entry - The locked codex entry.
+ * @returns A string describing how to unlock the entry.
+ */
+const buildUnlockHint = (entry: CodexEntry): string => {
+  const name = formatId(entry.sourceId);
+  switch (entry.sourceType) {
+    case "boss": return `Defeat ${name}`;
+    case "quest": return `Complete: ${name}`;
+    case "equipment": return `Obtain: ${name}`;
+    case "adventurer": return `Recruit a ${name}`;
+    case "upgrade": return `Purchase: ${name}`;
+    case "prestige": return `Purchase runestone upgrade: ${name}`;
+    case "zone": return `Explore: ${name}`;
+    case "exploration": return `Discover: ${name}`;
+    case "recipe": return `Craft: ${name}`;
+    default: return "Keep playing to unlock";
+  }
+};
+
 /**
  * Renders the codex panel with lore entries grouped by zone.
  * @returns The JSX element.
@@ -136,6 +170,9 @@ const CodexPanel = (): JSX.Element => {
                         <span className="codex-lock">{"🔒"}</span>
                         <span className="codex-entry-title">{"???"}</span>
                       </div>
+                      <p className="codex-unlock-hint">
+                        {buildUnlockHint(entry)}
+                      </p>
                     </div>
                   );
                 }