[codex] Fix bearer auth for remote Anthropic proxies

[zangqing828-ux]

What changed

This fixes Claude/Anthropic-compatible remote gateways that require Authorization: Bearer <token> even though they still speak the Anthropic API shape.

The patch adds a shared auth-header helper and uses it in:

• desktop connection testing
• provider validation
• runtime generation calls

For Anthropic wire requests against non-local, non-official hosts, Open CoDesign now sends both:

• x-api-key: <token>
• Authorization: Bearer <token>

Local Anthropic proxies and the official Anthropic endpoint stay on the existing behavior.

Root cause

Claude Code import preserved the Anthropic wire and remote base URL correctly, but runtime/auth header construction only emitted x-api-key for Anthropic requests. Some remote gateways accept Anthropic request/response shape while authenticating with Bearer tokens, which caused generation to fail with errors like 401 token not found.

Validation

• corepack pnpm --filter @open-codesign/providers test
• corepack pnpm --filter @open-codesign/desktop test -- --run src/main/connection-ipc.test.ts
• corepack pnpm typecheck
• corepack pnpm lint
• repo pre-commit hook: turbo run test
• repo pre-push hook: typecheck + lint