feat(core): port provider integrations to v2

[opencode-agent]

Summary

• port Azure, Cloudflare AI Gateway, Cloudflare Workers AI, DigitalOcean, GitLab, Poe, Snowflake Cortex, and xAI auth to the native V2 Integration registry
• add prompted key methods so provider metadata such as Azure resources, Cloudflare account/gateway IDs, and GitLab instance URLs is persisted with credentials
• preserve OAuth refresh, callback lifecycle, DigitalOcean router discovery, and provider-specific request behavior

GitLab

• replaces the legacy auth-package adapter with native PKCE OAuth, Integration-managed refresh, prompted PAT validation, and credential metadata
• keeps the existing GitLab provider/model routing intact

Validation

• 87 focused Core tests passed
• typechecks passed: Schema, Plugin, Protocol, Core, Server, Client, TUI, legacy JS SDK
• regenerated Client and legacy JS SDK surfaces
• git diff --check passed