feat(cli): add auth command to list authenticated providers - #34514

What

Adds a top-level auth command to the V2 CLI that lists which providers are currently authenticated.

$ opencode auth
Amazon Bedrock  AWS_REGION · env
Google          GEMINI_API_KEY · env
OpenCode        anomaly · credential

When nothing is authenticated it prints No authenticated providers.

Why

The V2 CLi (packages/cli) had no way to see authenticated providers — the legacy auth list / providers list command was never ported. V2 already models auth as integrations with connections, exposed over the server API (integration.list) and used by the TUI's connect-provider flow, but nothing surfaced it on the command line.

How

Thin handler over the existing typed client, mirroring the debug agents handler:

• client.v2.integration.list({ location: { directory } })
• Keep only integrations with a non-empty connections array (i.e. authenticated).
• Render one line per connection: credential connections show their label, env connections show the active environment variable name.

No backend or server changes are needed. The command name is intentionally simple and leaves room for future auth login / auth logout subcommands.

Verification

• bun typecheck from packages/cli.
• bun dev auth against a real running server lists the connected providers shown above; bun dev --help lists the new command.