fix(explorer): make SFTP/SCP upload button open the file picker (#69)

[macnev2013]

Problem

Clicking Explorer → Upload file did nothing (#69).

The SFTP/SCP upload handler loaded the dialog plugin via Function("s","return import(s)")(specifier). A Function-eval'd import() resolves its bare specifier (@tauri-apps/plugin-dialog) against the document base URL rather than the module's resolution scope, so it throws. The catch then fell back to window.prompt(...) — a no-op in Tauri's macOS WKWebView — so the click produced no visible result.

The S3 browser and the SFTP drag-and-drop path both already use the correct await import("@tauri-apps/plugin-dialog"), which is why those worked (and why drag-drop was the maintainer's suggested workaround).

This slipped past CI because the e2e upload specs invoke the backend command directly — the native OS file picker can't be driven by WebdriverIO.

Fix

• Use a plain await import("@tauri-apps/plugin-dialog") with open({ multiple: true }), so multiple files can be selected at once.
• Route the selection through enqueue_upload (same path as drag-and-drop) instead of the single-file upload command: it walks directories (so folders work too), reports progress in the transfer overlay, and the existing completion listener refreshes the listing — so the premature immediate reload is dropped.
• Works for both SFTP and SCP (the view is shared); both sftp_enqueue_upload and scp_enqueue_upload exist with matching arg shapes, and dialog:default already grants allow-open.

Tests

• New ExplorerView.upload.test.tsx: picker→enqueue flow, single-path normalization, and the cancelled-picker case.
• tsc --noEmit clean; full Vitest suite passing.

Addresses #69