feat: folders and files the assistant cannot take, dropped from a file pane, go into the message as their paths; a file that fails shows a red note over the field, fading in and out like an error toast

internal/server/web/static/app.css

@@ -922,8 +922,11 @@ body.touch.term-active .ai-fab { bottom:104px; }
 .ai-file-chip span { overflow:hidden; text-overflow:ellipsis; white-space:nowrap; }
 .ai-file-chip button { flex:none; width:18px; height:18px; padding:0; border:0; border-radius:50%; background:transparent; color:var(--muted); line-height:1; }
 .ai-file-chip button:hover { color:var(--text); background:#303846; }
-.ai-file-picker { position:absolute; right:10px; bottom:78px; z-index:5; display:flex; flex-direction:column; gap:3px; max-width:min(320px, calc(100% - 20px)); max-height:45%; overflow:auto; padding:9px; background:var(--panel); border:1px solid var(--border); border-radius:10px; box-shadow:0 8px 24px rgba(0,0,0,.45); }
-.ai-file-picker[hidden] { display:none; }
+.ai-file-error { position:absolute; left:12px; right:12px; bottom:12px; z-index:3; padding:10px 14px; border:1px solid #6b2b2b; border-radius:8px;
+                 background:#3a1d1d; color:#ffb3b3; font-size:13px; line-height:1.4; text-align:center; overflow-wrap:anywhere;
+                 box-shadow:0 8px 24px rgba(0,0,0,.4); opacity:0; transform:translateY(8px); pointer-events:none;
+                 transition:opacity .2s ease, transform .2s ease; }
+.ai-file-error.show { opacity:1; transform:none; }
 .ai-form-in.drag .ai-inputbox { border-color:var(--accent); background:#111a28; box-shadow:0 0 0 3px rgba(91,140,255,.24), 0 0 18px rgba(91,140,255,.16); }
 .ai-form-in.drag .ai-inputbox::after { content:'Отпустите файл, чтобы прикрепить'; position:absolute; inset:3px; z-index:4; display:grid; place-items:center; padding:8px; border:1px dashed rgba(157,184,255,.75); border-radius:9px; background:rgba(23,43,72,.88); color:#dce7ff; font-size:12px; font-weight:550; text-align:center; pointer-events:none; }
 @media (max-width: 640px) {