docs(tools): add video_generate / video_gen toolset to user-facing tool docs (#27050)

The video_gen toolset and its video_generate tool shipped without
user-facing reference docs. toolsets-reference.md and the dev-guide
plugin page were already in, but reference/tools-reference.md had no
video_gen section at all and user-guide/features/tools.md's Media row
didn't list video_generate.

- reference/tools-reference.md: add a video_gen section after video,
  including backend list (xAI Grok-Imagine, FAL.ai Veo/Pixverse/Kling),
  unified text-to-video / image-to-video surface note, link to the
  dev-guide plugin page, and the video_generate tool row. Add
  video_generate to the standalone-tools quick-counts line.
- user-guide/features/tools.md: extend Media row with video_generate
  and video_analyze plus an opt-in caveat.

website/docs/user-guide/features/tools.md

@@ -24,7 +24,7 @@ High-level categories:
 | **X Search** | `x_search` | Search X (Twitter) posts and threads via xAI's built-in `x_search` Responses tool — gated on xAI credentials (SuperGrok OAuth or `XAI_API_KEY`); off by default, opt in via `hermes tools` → 🐦 X (Twitter) Search. |
 | **Terminal & Files** | `terminal`, `process`, `read_file`, `patch` | Execute commands and manipulate files. |
 | **Browser** | `browser_navigate`, `browser_snapshot`, `browser_vision` | Interactive browser automation with text and vision support. |
-| **Media** | `vision_analyze`, `image_generate`, `text_to_speech` | Multimodal analysis and generation. |
+| **Media** | `vision_analyze`, `image_generate`, `video_generate`, `video_analyze`, `text_to_speech` | Multimodal analysis and generation. `video_generate` and `video_analyze` are opt-in (add `video_gen` / `video` toolsets via `hermes tools` or `--toolsets`). |
 | **Agent orchestration** | `todo`, `clarify`, `execute_code`, `delegate_task` | Planning, clarification, code execution, and subagent delegation. |
 | **Memory & recall** | `memory`, `session_search` | Persistent memory and session search. |
 | **Automation & delivery** | `cronjob`, `send_message` | Scheduled tasks with create/list/update/pause/resume/run/remove actions, plus outbound messaging delivery. |