fix(oauth): honor discovered CIMD support - #1732

Summary

Prefer Client ID Metadata Documents when OAuth discovery advertises CIMD, including servers that also expose dynamic client registration. Automatic MCP OAuth now follows the server-advertised client path instead of incorrectly asking the user for manual app registration.

Flow

reserve popup -> probe OAuth discovery
  -> CIMD: create or reuse metadata client -> start OAuth
  -> otherwise DCR: register client -> start OAuth
  -> otherwise: show manual client setup

The UI consumes the SDK canonical OAuthProbeResult, preventing discovery capabilities from being dropped by a duplicated UI-only type.

Validation

• React add-account modal suite: 45 tests passed.
• React and SDK typecheck, format, and lint passed.
• Selfhost MCP OAuth CIMD browser E2E passed with recording and trace.
• All 36 applicable GitHub CI checks passed at 4e3b63f69.