feat: drag files between file panes (move or copy, SSH hosts too) and into a terminal of the same machine

internal/server/web/static/app.css

@@ -342,6 +342,8 @@ body.split1 .float-add { top:42px; right:16px; }
 body.multi .float-add { opacity:0; pointer-events:none; }
 .tabview { position:absolute; inset:8px; opacity:0; visibility:hidden; transform:translateY(4px) scale(.995);
            transition:opacity .22s ease, transform .22s ease, visibility 0s .22s; }
+/* A tab fading out takes no pointer: a drop goes to the tab coming in. */
+.tabview:not(.on) { pointer-events:none; }
 .tabview.on { opacity:1; visibility:visible; transform:none; transition:opacity .22s ease, transform .22s ease, visibility 0s; }
 .pane { position:absolute; display:flex; flex-direction:column; border-radius:7px; overflow:hidden;
         transition:left .26s ease, top .26s ease, width .26s ease, height .26s ease, border-color .2s; }
@@ -373,6 +375,18 @@ body:not(.touch) .tabview:not(.split) .xterm .xterm-viewport { right:-7px; }
               box-shadow:0 12px 30px rgba(0,0,0,.55); transition:transform .04s linear; }
 .drag-ghost[data-hint]:not([data-hint=""])::after { content:attr(data-hint); display:block; margin-top:3px; font-size:11px; color:var(--muted); }
 body.dnd, body.dnd * { cursor:grabbing !important; }
+/* Files dragged out of a pane: the target's outline, and the small window
+   where they were dropped. */
+.hint.drophint { position:fixed; z-index:55; transition:none; }
+.dropdlg { position:fixed; z-index:56; width:300px; max-width:calc(100vw - 16px); padding:12px; display:flex; flex-direction:column; gap:8px;
+           background:var(--panel); border:1px solid var(--border); border-radius:10px; box-shadow:0 14px 36px rgba(0,0,0,.55); font-size:13px; }
+.dropdlg[hidden] { display:none; }
+.dropdlg .dd-what { font-weight:600; overflow:hidden; text-overflow:ellipsis; white-space:nowrap; }
+.dropdlg .dd-to { overflow-wrap:anywhere; }
+.dropdlg .dd-c { display:flex; align-items:center; gap:6px; }
+.dropdlg .mv-prog { margin-top:0; }
+.dropdlg .dd-btns { display:flex; gap:6px; justify-content:flex-end; }
+.fpane .fp-list tr[data-name] { user-select:none; }
 .empty { position:absolute; inset:0; display:flex; flex-direction:column; align-items:center; justify-content:center; gap:12px; color:var(--muted); }
 .empty[hidden] { display:none; }
 /* The "+" menu: a terminal here, or on another machine. */