SiYuan: Stored XSS to RCE via attribute-view cell rendering in genAVValueHTML()

The attribute-view (database) cell renderer `genAVValueHTML` interpolates cell content raw in four of its branches: `text`, `url`, `phone`, and `mAsset`. A cell value like `</textarea><img src=x onerror="...">` or `"><img src=x onerror="...">` breaks out of its surrounding tag and runs arbitrary JavaScript in the renderer when the victim opens the block-attribute panel. On Electron desktop the renderer runs with `nodeIntegration:true`, so the XSS chains to host RCE via `require('child_process')`. AV files live under the workspace and ride normal sync, so an attacker with write access to any synced workspace plants the payload once and it fires on every device that opens a panel containing that row. The kernel doesn't escape on the way in either, so the malicious cell persists byte-for-byte. There's no equivalent of the `html.EscapeAttrVal` call that protects block IAL attributes at `kernel/model/blockial.go:261`. Companion advisory: GHSA-mvjr-vv3c-w4qv. Same workspace-sync to renderer-sink to Electron-RCE pattern in the CSS-snippet renderer, different sink file. Worth auditing for the same pattern in other renderers that pull from synced workspace data.