Prevent duplicate issue upvotes
Fixes duplicate upvote inflation by adding persistent browser voter IDs, disabling already-used upvote buttons, and storing backend upvoter IDs per issue so repeat PATCH requests do not increment counts.
Fixes duplicate upvote inflation by adding persistent browser voter IDs, disabling already-used upvote buttons, and storing backend upvoter IDs per issue so repeat PATCH requests do not increment counts.