Feat/litellm provider (#12823)

* feat: add LiteLLM provider types, env var, credentials, and auth choice

Add litellm-api-key auth choice, LITELLM_API_KEY env var mapping,
setLitellmApiKey() credential storage, and LITELLM_DEFAULT_MODEL_REF.

* feat: add LiteLLM onboarding handler and provider config

Add applyLitellmProviderConfig which properly registers
models.providers.litellm with baseUrl, api type, and model definitions.
This fixes the critical bug from PR #6488 where the provider entry was
never created, causing model resolution to fail at runtime.

* docs: add LiteLLM provider documentation

Add setup guide covering onboarding, manual config, virtual keys,
model routing, and usage tracking. Link from provider index.

* docs: add LiteLLM to sidebar navigation in docs.json

Add providers/litellm to both English and Chinese provider page lists
so the docs page appears in the sidebar navigation.

* test: add LiteLLM non-interactive onboarding test

Wire up litellmApiKey flag inference and auth-choice handler for the
non-interactive onboarding path, and add an integration test covering
profile, model default, and credential storage.

* fix: register --litellm-api-key CLI flag and add preferred provider mapping

Wire up the missing Commander CLI option, action handler mapping, and
help text for --litellm-api-key. Add litellm-api-key to the preferred
provider map for consistency with other providers.

* fix: remove zh-CN sidebar entry for litellm (no localized page yet)

* style: format buildLitellmModelDefinition return type

* fix(onboarding): harden LiteLLM provider setup (#12823)

* refactor(onboarding): keep auth-choice provider dispatcher under size limit

---------

Co-authored-by: Peter Steinberger <steipete@gmail.com>

CHANGELOG.md

@@ -43,6 +43,7 @@ Docs: https://docs.openclaw.ai
 - Telegram: match DM `allowFrom` against sender user id (fallback to chat id) and clarify pairing logs. (#12779) Thanks @liuxiaopai-ai.
 - Pairing/Telegram: include the actual pairing code in approve commands, route Telegram pairing replies through the shared pairing message builder, and add regression checks to prevent `<code>` placeholder drift.
 - Onboarding: QuickStart now auto-installs shell completion (prompt only in Manual).
+- Onboarding/Providers: add LiteLLM provider onboarding and preserve custom LiteLLM proxy base URLs while enforcing API-key auth mode. (#12823) Thanks @ryan-crabbe.
 - Docker: make `docker-setup.sh` compatible with macOS Bash 3.2 and empty extra mounts. (#9441) Thanks @mateusz-michalik.
 - Auth: strip embedded line breaks from pasted API keys and tokens before storing/resolving credentials.
 - Agents: strip reasoning tags and downgraded tool markers from messaging tool and streaming output to prevent leakage. (#11053, #13453) Thanks @liebertar, @meaadore1221-afk, @gumadeiras.