Motivation

• Add first-class support for DeepSeek so users with only a DeepSeek account can authenticate and use DeepSeek models directly instead of routing through aggregators.
• Make DeepSeek discoverable from env/profiles and integrable into the existing onboarding flows (interactive and non-interactive).

Description

• Added a DeepSeek model catalog and constants in src/agents/deepseek-models.ts and exposed DEEPSEEK_BASE_URL and DEEPSEEK_DEFAULT_MODEL_REF for wiring.
• Wired implicit provider discovery so deepseek is auto-registered when DEEPSEEK_API_KEY or a deepseek auth profile exists in src/agents/models-config.providers.ts and added env var mapping in src/agents/model-auth.ts.
• Implemented provider config appliers and default-model helpers in src/commands/onboard-auth.config-core.ts and credential helper setDeepseekApiKey in src/commands/onboard-auth.credentials.ts.
• Extended onboarding types, CLI flags and onboarding command plumbing to accept deepseek-api-key / --deepseek-api-key in src/commands/onboard-types.ts and src/cli/program/register.onboard.ts.
• Added DeepSeek to auth-choice UX: grouped option + preferred provider mapping + interactive application flow (prompts and profile creation) in src/commands/auth-choice-options.ts, src/commands/auth-choice.preferred-provider.ts, and src/commands/auth-choice.apply.api-providers.ts.
• Hooked non-interactive onboarding inference & application for DeepSeek in src/commands/onboard-non-interactive/local/* and src/commands/onboard-non-interactive/local/auth-choice-inference.ts.
• Added tests to cover implicit provider generation and CLI wiring and updated smoke/unit tests to include DeepSeek cases (src/agents/models-config.skips-writing-models-json-no-env-token.test.ts, src/cli/program.smoke.test.ts, src/commands/auth-choice-options.test.ts).
• Added documentation docs/providers/deepseek.md and linked it from docs/providers/index.md.

Testing

• Ran targeted unit tests: pnpm test -- src/agents/models-config.skips-writing-models-json-no-env-token.test.ts src/cli/program.smoke.test.ts src/commands/auth-choice-options.test.ts, all tests passed (Test Files: 3, Tests: 32 passed).
• Verified TypeScript checks with pnpm tsgo, which completed successfully.
• Ran formatting with pnpm format to update style, which completed successfully.

Codex Task