Case handling for `Choice` help output (values forced to lowercase)

Expected Behavior

Values passed to click.Choice should preserve their original casing when displayed in --help output.

Example:

--brokerage [Interactive Brokers|Tradier|Oanda|Bitfinex|Coinbase Advanced Trade|Binance|Zerodha|Samco|Terminal Link|Trading Technologies|Kraken|CharlesSchwab|IQFeed|Polygon|CoinApi|ThetaData|Custom data only|Bybit|TradeStation|Alpaca|Tastytrade|Eze]

Actual Behavior

Since Click 8.2.0, all values are displayed in lowercase, regardless of how they were registered:

--brokerage [paper trading|interactive brokers|tradier|oanda|bitfinex|coinbase advanced trade|binance|zerodha|samco|terminal link|trading technologies|kraken|charlesschwab|bybit|tradestation|alpaca|tastytrade|eze]

This misleads users into thinking only lowercase values are accepted.

Potential Solution

• create custom class MyChoice(Choice)
  • override get_metavar(...)
• Continue using case-folding for parsing input when case_sensitive=False.
• The regression likely comes from PR #2796, which lowercases values when registering.

Reproducing the Problem

• run: lean live deploy --help

• Click 8.1.8: casing preserved ✅

• Click 8.2.0+: values all lowercase ❌

System Information

• Click version(s): 8.2.0, 8.2.1 (regression)
• Last working version: 8.1.8
• OS: All (confirmed on Windows 10, Ubuntu 22.04)
• Python: 3.11

Checklist

• I have completely filled out this template
• I have confirmed that this issue exists on the current master branch
• I have confirmed that this is not a duplicate issue by searching issues

• I have provided detailed steps to reproduce the issue

Reproduce the regression with lean live deploy --help, comparing Click 8.1.8 with 8.2.0 or 8.2.1. Start by reviewing Click Choice behavior and the registration change in PR #2796. Done means help output preserves the registered casing while case-insensitive parsing still works.