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/reference/slash-commands.md

@@ -83,6 +83,7 @@ Type `/` in the CLI to open the autocomplete menu. Built-in commands are case-in
 | `/image <path>` | Attach a local image file for your next prompt. |
 | `/debug` | Upload debug report (system info + logs) and get shareable links. Also available in messaging. |
 | `/profile` | Show active profile name and home directory |
+| `/gquota` | Show Google Gemini Code Assist quota usage with progress bars (only available when the `google-gemini-cli` provider is active). |
 
 ### Exit