fix: check response.ok before parsing JSON in fetch calls

Fix JSON parsing errors when server returns non-JSON responses:
- Check response.ok before calling response.json()
- Add fallback error messages using status text
- Apply fix to all fetch calls across 12 components

This prevents 'JSON.parse: unexpected character' errors when
server returns HTML error pages or other non-JSON responses.

src/app/admin/players/page.tsx

@@ -64,6 +64,16 @@ export default function AdminPlayersPage() {
         body: JSON.stringify({ name: newName.trim() }),
       })
 
+      if (!response.ok) {
+        try {
+          const errorData = await response.json()
+          alert(`Error: ${errorData.error || 'Failed to update player'}`)
+        } catch {
+          alert(`Error: ${response.status} ${response.statusText}`)
+        }
+        return
+      }
+
       const data = await response.json()
 
       if (data.success) {
@@ -105,6 +115,16 @@ export default function AdminPlayersPage() {
         }),
       })
 
+      if (!response.ok) {
+        try {
+          const errorData = await response.json()
+          alert(`Error: ${errorData.error || 'Failed to merge players'}`)
+        } catch {
+          alert(`Error: ${response.status} ${response.statusText}`)
+        }
+        return
+      }
+
       const data = await response.json()
 
       if (data.success) {
@@ -117,7 +137,7 @@ export default function AdminPlayersPage() {
         alert(`Error: ${data.error}`)
       }
     } catch (err: unknown) {
-      alert(`Error: ${err instanceof Error ? err.message : 'Unknown error occurred'}`)
+      alert(`Error: ${err instanceof Error ? err.message : "Unknown error occurred"}`)
     } finally {
       setIsMerging(false)
     }
@@ -134,6 +154,16 @@ export default function AdminPlayersPage() {
         method: "DELETE",
       })
 
+      if (!response.ok) {
+        try {
+          const errorData = await response.json()
+          alert(`Error: ${errorData.error || 'Failed to delete player'}`)
+        } catch {
+          alert(`Error: ${response.status} ${response.statusText}`)
+        }
+        return
+      }
+
       const data = await response.json()
 
       if (data.success) {
@@ -142,7 +172,7 @@ export default function AdminPlayersPage() {
         alert(`Error: ${data.error}`)
       }
     } catch (err: unknown) {
-      alert(`Error: ${err instanceof Error ? err.message : "Unknown error occurred"}`)
+      alert(`Error: ${err instanceof Error ? err.message : 'Unknown error occurred'}`)
     } finally {
       setDeletingId(null)
     }