[Feature]: Workspace file viewer for images, video, audio, and PDF with sidebar actions

[DenizAltunkapan]

Problem

Cloud Page can list and download files, but there is no way to open most of them in the browser. To look at an image, watch a short video, listen to an audio file, or read a PDF, the user has to download it first. This makes the cloud feel like a file dump rather than a workspace, and it leaves no natural place for per-file actions (share, rename, delete, favorite, comment) to live.

Example: a user opens a folder of holiday photos. Today they download each one to preview it. They should be able to click a photo, see it inline, step through the folder, and act on it from one place.

Proposed solution

Add a workspace file viewer that opens a file inline based on its type, with a consistent actions sidebar around it.

Scope:

• inline rendering for common types: images, video, audio, and PDF
• a shared viewer shell so every file type opens through the same component, with a per-type renderer (this same shell is intended to host the Markdown workspace editor, tracked separately, so it should be built to be extended rather than image/video-only)
• a sidebar with per-file actions: rename, move, delete, download, and space for future actions (share, favorite, comment)
• next/previous navigation within the current folder, so a folder of images behaves like a gallery
• graceful fallback for unsupported types (offer download instead of a broken preview)
• respect the existing path validation and user boundary; the viewer must not expose files outside the user root

Acceptance criteria

• Images, video, audio, and PDF files open inline in the browser without downloading first.
• Unsupported file types show a clean fallback with a download option, never a broken view.
• The viewer exposes rename, move, delete, and download for the open file.
• Users can move to the next and previous file in the folder from the viewer.
• The viewer is built as a reusable shell that other file types (for example a Markdown editor) can plug into.
• Files outside the user root are never reachable through the viewer.
• Loading and error states are handled cleanly.

Related: builds on the file preview work (Vault-Web/vault-web#262, Vault-Web/vault-web#235). The sidebar is the natural home for sharing (#27), favorites, and comments once those land.