Allow dropping images and files to paste into the standalone app

[nedtwigg]

Background

Dragging and dropping on a terminal pane has two use cases:

1. Drop a file or image to paste its path into the terminal.
2. Drag a pane tab to rearrange the pane layout.

In the VS Code extension only (2) works — file/image drop into a webview is blocked by VS Code itself, which is a platform limitation we can't change.

In the standalone Tauri app we previously had only (1): file/image drop pasted paths, but pane drag did not work. This was because Tauri 2's dragDropEnabled: true (the default) captures OS drag-drop natively, and on Windows that blocks all HTML5 drag events — including internal Dockview pane reorder. See tauri-apps/tauri#8581 and tauri-apps/tauri#14373.

We've now set dragDropEnabled: false, which restores pane drag (case 2). The cost is that case (1) is currently broken in standalone too: Chromium's webview doesn't expose File.path, so a vanilla HTML5 drop can't recover the path string without OS-level cooperation.

What we want

Re-enable file/image drop-to-paste in the standalone without re-breaking pane drag.

Blocker

Depends on upstream Tauri offering a way to receive file paths from native OS drops while still letting HTML5 drag events flow to the webview. Tracked upstream at tauri-apps/tauri#14373. Once that lands (or a usable plugin/escape hatch appears) we can flip dragDropEnabled back on (or adopt the new API) and re-activate the stubs.

Stubs left in the codebase

Wiring is intentionally left in place so re-enabling is a small change:

• standalone/src-tauri/tauri.conf.json — dragDropEnabled: false is the kill switch.
• standalone/src-tauri/src/lib.rs — the WindowEvent::DragDrop handler that emits mouseterm://files-dropped.
• standalone/src/tauri-adapter.ts — the mouseterm://files-dropped listener and onFilesDropped plumbing.
• lib/src/lib/platform/types.ts — the optional onFilesDropped interface method.
• lib/src/components/wall/use-session-persistence.ts — the platform.onFilesDropped?.(…) subscription that calls pasteFilePaths.

Note on VS Code

Doesn't apply to the VS Code extension — file drop into VS Code webviews is outside our control.