Add connect --emulator shortcut with HTTPS/HTTP fallback

[mkrueger]

Refs #74.

Reduces friction in using the shell with the Cosmos DB Emulator.

What

• Adds a connect --emulator (alias -e) shortcut and a startup --connect-emulator option.
  • Defaults the endpoint to https://localhost:8081/ when no connection string is given.
  • Uses the well-known emulator key and gateway mode (existing behavior, just easier to invoke).
  • Refuses to be combined with non-local endpoints to keep behavior predictable.
• On TLS handshake failure against an emulator endpoint, the shell now retries once over HTTP and reports which protocol was actually used.
• When the connection ends up on HTTP, the shell prints a hint that the Cosmos DB emulator Docker image accepts --protocol [https|http], which lets users skip TLS cert setup entirely.

Why

Issue #74 tracks the rough first-use experience with the emulator: users have to deal with self-signed cert imports, switching protocols, and re-typing the well-known key/connection string. With this change the simplest path is now connect --emulator (or cosmosdbshell --connect-emulator) and we surface the HTTPS-vs-HTTP situation explicitly instead of silently failing.

Safety

The HTTPS → HTTP fallback is intentionally scoped: it only triggers when --emulator is used (or an emulator endpoint is auto-detected), the original scheme is HTTPS, and the failure is a TLS handshake / cert-validation error. We don't downgrade arbitrary HTTPS endpoints.

Validation

• dotnet build CosmosDBShell/CosmosDBShell.csproj — green
• dotnet test CosmosDBShell.Tests/CosmosDBShell.Tests.csproj --filter "Category!=Emulator" — 872 passed (4 new connect tests added)
• Manual: connect --emulator shows up in help connect with the new example.

[Copilot]

Pull request overview

This PR improves the first-run experience for using CosmosDBShell with the Azure Cosmos DB Emulator by adding explicit emulator connection shortcuts and implementing an emulator-scoped HTTPS→HTTP fallback when TLS negotiation fails.

Changes:

• Added connect --emulator / -e and startup --connect-emulator, defaulting to https://localhost:8081/ with emulator well-known key + gateway mode.
• Implemented an emulator-only retry over HTTP when an HTTPS connection fails due to a detected TLS handshake/certificate problem, and prints which protocol was used.
• Updated docs/localization and added tests for option binding and non-local endpoint rejection.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
README.md	Documents the new --connect-emulator startup option.
docs/connect.md	Adds emulator shortcut examples and explains protocol reporting/tip.
CosmosDBShell/Program.cs	Wires --connect-emulator into startup connect flow.
CosmosDBShell/lang/en.ftl	Adds localized strings for emulator option, errors, and protocol reporting.
CosmosDBShell/Azure.Data.Cosmos.Shell.Util/LocalizableSentenceBuilder.cs	Exposes the localized help string for the new startup option.
CosmosDBShell/Azure.Data.Cosmos.Shell.Core/ShellInterpreter.cs	Implements forceEmulator, endpoint defaulting, and HTTPS→HTTP fallback logic.
CosmosDBShell/Azure.Data.Cosmos.Shell.Commands/ConnectCommand.cs	Adds --emulator / -e and routes it to ShellInterpreter.ConnectAsync.
CosmosDBShell.Tests/CommandTests/ConnectCommandTests.cs	Adds tests for emulator flag binding and non-local endpoint rejection.

Comments suppressed due to low confidence (1)

CosmosDBShell/Azure.Data.Cosmos.Shell.Commands/ConnectCommand.cs:103

• The JSON result for connect sets ["connected state"] based on the input ConnectionString. When using connect --emulator with no explicit endpoint this becomes null, and when an HTTPS→HTTP fallback occurs it will still report the original HTTPS endpoint rather than the actual connected endpoint. Consider using the post-connect state (e.g., ((ConnectedState)shell.State).Client.Endpoint) so the result reflects the real connection.

            var endpoint = this.ConnectionString is null
                ? null
                : ParsedDocDBConnectionString.ExtractEndpoint(this.ConnectionString);
            var resultElement = JsonSerializer.SerializeToElement(new Dictionary<string, string?>
            {
                ["connected state"] = endpoint,
            });