Feat(aigw) set dummy creds for qwen and codex

[jbaross]

Relates to #6671

Setting these dummy keys as part of the prerequisites obscures their purpose so instead I have folded them into the command to run the cli tool. This is similar to how we set CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS=1 for running bedrock models and makes it clear to a user why this is set.

For changes to the validation ruby and snippet logic, these are patterned after the corresponding claude code files.

Description

Fixes #issue

Preview Links

https://deploy-preview-6748--kongdeveloper.netlify.app/ai-gateway/ai-clis/

Checklist

• Tested how-to docs. If not, note why here.
• All pages contain metadata.
• Any new docs link to existing docs.
• All autogenerated instructions render correctly (API, decK, Konnect, Kong Manager).
• Style guide (capitalized gateway entities, placeholder URLs) implemented correctly.
• Every page has a description entry in frontmatter.
• Add new pages to the product documentation index (if applicable).

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[lmilan]

I'm getting this error:

⚠ MCP client for codex_apps failed to start: MCP startup failed: handshaking
with MCP server failed: Send message error Transport
[codex_rmcp_client::event_notification_transport::EventNotificationTransport<r
mcp::transport::worker::WorkerTransport<rmcp::transport::streamable_http_clien
t::StreamableHttpClientWorker<codex_rmcp_client::http_client_adapter::Streamab
leHttpClientAdapter>>>] error: unexpected server response: HTTP 401: {
"error": {
"message": "Could not parse your authentication token. Please try signing
in again.",
"type": null,
"code": "unauthorized_unknown",
"param": null
},
"status": 401
}, when send initialize request
⚠ MCP startup incomplete (failed: codex_apps)