docs: backfill coverage for recently-merged features (#11942)

Fills documentation gaps that accumulated as features merged ahead of their
docs updates. All additions are verified against code and the originating PRs.

Providers:
- Ollama Cloud (#10782) — new provider section, env vars, quickstart/fallback rows
- xAI Grok Responses API + TTS (#10783) — provider note, TTS table + config
- Google Gemini CLI OAuth (#11270) — quickstart/fallback/cli-commands entries
- NVIDIA NIM (#11774) — NVIDIA_API_KEY / NVIDIA_BASE_URL in env-vars reference
- HERMES_INFERENCE_PROVIDER enum updated

Messaging:
- DISCORD_ALLOWED_ROLES (#11608) — env-vars, discord.md access control section
- DingTalk QR device-flow (#11574) — wizard path in Option A + openClaw disclosure
- Feishu document comment intelligent reply (#11898) — full section + 3-tier access control + CLI

Skills / commands:
- concept-diagrams skill (#11363) — optional-skills-catalog entry
- /gquota (#11270) — slash-commands reference

Build: docusaurus build passes, ascii-guard lint 0 errors.

website/docs/user-guide/features/fallback-providers.md

@@ -48,6 +48,9 @@ Both `provider` and `model` are **required**. If either is missing, the fallback
 | MiniMax (China) | `minimax-cn` | `MINIMAX_CN_API_KEY` |
 | DeepSeek | `deepseek` | `DEEPSEEK_API_KEY` |
 | NVIDIA NIM | `nvidia` | `NVIDIA_API_KEY` (optional: `NVIDIA_BASE_URL`) |
+| Ollama Cloud | `ollama-cloud` | `OLLAMA_API_KEY` |
+| Google Gemini (OAuth) | `google-gemini-cli` | `hermes model` (Google OAuth; optional: `HERMES_GEMINI_PROJECT_ID`) |
+| xAI (Grok) | `xai` (alias `grok`) | `XAI_API_KEY` (optional: `XAI_BASE_URL`) |
 | OpenCode Zen | `opencode-zen` | `OPENCODE_ZEN_API_KEY` |
 | OpenCode Go | `opencode-go` | `OPENCODE_GO_API_KEY` |
 | Kilo Code | `kilocode` | `KILOCODE_API_KEY` |