docs(accessories): add 4K HDMI IN to MIPI CSI-2 Adapter guide

[tzz-radxa]

What this PR does

Adds documentation for the Radxa 4K HDMI IN to MIPI CSI-2 Adapter under accessories/display, following the structure of accessories/heatsink-case/metal-case-1290 (product intro README.md + usage tutorial page).

• docs/accessories/display/hdmi-in-to-mipi-csi2/README.md — product introduction (based on RK628H), features, specifications, mechanical dimensions and package contents
• docs/accessories/display/hdmi-in-to-mipi-csi2/hdmi-in-to-mipi-csi2-rock-4d.md — Using with ROCK 4D (hardware connection, overlay enablement, device check, HDMI video/audio capture, FAQ)
• docs/common/accessories/_hdmi-in-to-mipi-csi2-usage.mdx — the tutorial body extracted into a parameterized partial, so the same tutorial can be reused for other boards by passing props instead of copying the whole page
• also renames the display category title from 高清显示屏 to 高清显示, since the category now also covers an HDMI-in video adapter rather than only screens

All changes are mirrored in i18n/en/.

Parameterized tutorial (reuse for other boards)

The tutorial body lives in docs/common/accessories/_hdmi-in-to-mipi-csi2-usage.mdx and is imported by a thin per-board page, in the same style as the camera tutorials (common/accessories/_camera-*.mdx). A new board page only needs to pass props:

Prop	Meaning	ROCK 4D value
product	board name shown in the text	ROCK 4D
board	board id used in the command prompt	rock-4d
audio_bus	I2S bus used for HDMI audio capture	SAI2_M0
video_dev	video capture node	/dev/video0
video_overlay	rsetup overlay for HDMI video	Enable Radxa 4K HDMI IN to MIPI CSI-2 Adapter on 4-lane CSI
audio_overlay	rsetup overlay for HDMI audio	Enable SAI2-M0 capture-only dummy sound card
audio_capture_card	ALSA capture card name	sai2capture
audio_playback_card	ALSA playback card name	rockchipes8388
video_dtbo / audio_dtbo	dtbo names used in the FAQ check	rock-4d-radxa-hdmi-in-4k-rk628.dtbo / rk3576-sai2-2ch-m0-capture-only.dtbo
video_connection_img / audio_connection_img / preview_img	hardware connection and preview screenshots	ROCK 4D images

Adding support for another board is then a new small page (title + prop block), with no duplicated body.

Evidence / sources

• product material provided internally (product overview, specification table, mechanical drawing, package contents)
• ROCK 4D usage tutorial provided internally (hardware connection photos, overlay names, commands, FAQ)
• hardware interface context cross-checked against docs/rock4/rock4d/hardware-use/mipi-csi.md

Notes

• tutorial commands are examples verified on ROCK 4D; where the video node or sound card depends on the system, the FAQ explains how to look them up instead of hard-coding values
• no supply-chain information (part numbers / vendors) is included