v0.6.0: per-artifact actions menu (⋯ + right-click)

A ⋯ button on row hover and right-click on a feed row open the same floating
menu: Keep / Open / Copy link / Delete. Dismisses on click-away/Escape,
edge-flips to stay on-screen. Standalone one-click Delete icon stays; the
Trash view keeps its dedicated Undelete.

- Row markup: actions grouped in a .row-actions container (delete + ⋯ in the
  feed/keep views; undelete in trash). Reuses the existing keep endpoint.
- Menu only in the normal/keep views, not trash. Keep-toggle syncs the row's
  kept badge + the preview Keep button, and (in the Keep folder) drops the row
  when unkept.
- Frontend-only (no backend change); inline JS validated with node --check;
  152 tests pass; feed renders in all views.

Share + Add-label join the menu in later slices.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

static/agentfeed.css

@@ -1060,12 +1060,22 @@ kbd {
   position: relative;
 }
 
-.row-action {
+.row-actions {
   position: absolute;
-  right: 0.5rem;
+  right: 0.4rem;
   top: 50%;
   transform: translateY(-50%);
+  display: flex;
+  gap: 0.15rem;
   opacity: 0;
+}
+
+.artifact-row:hover .row-actions,
+.artifact-row:focus-within .row-actions {
+  opacity: 1;
+}
+
+.row-action {
   cursor: pointer;
   font-size: 0.95rem;
   line-height: 1;
@@ -1075,11 +1085,6 @@ kbd {
   color: var(--muted);
 }
 
-.artifact-row:hover .row-action,
-.artifact-row:focus-within .row-action {
-  opacity: 1;
-}
-
 .row-action:hover {
   background: var(--surface-alt);
   color: var(--text);
@@ -1089,6 +1094,43 @@ kbd {
   color: var(--danger-text-plain);
 }
 
+/* Per-row actions menu (opened by the ⋯ trigger or right-click) */
+.row-menu {
+  position: fixed;
+  z-index: 100;
+  min-width: 9rem;
+  background: var(--surface);
+  border: 1px solid var(--control-border);
+  border-radius: 8px;
+  box-shadow: 0 6px 18px rgba(0, 0, 0, 0.14);
+  padding: 0.25rem;
+  display: flex;
+  flex-direction: column;
+}
+
+.row-menu[hidden] {
+  display: none;
+}
+
+.row-menu button {
+  background: transparent;
+  border: 0;
+  border-radius: 5px;
+  color: var(--text);
+  cursor: pointer;
+  font-size: 0.85rem;
+  padding: 0.4rem 0.6rem;
+  text-align: left;
+}
+
+.row-menu button:hover {
+  background: var(--surface-alt);
+}
+
+.row-menu button.danger {
+  color: var(--danger-text-plain);
+}
+
 /* System folders (Keep / Deleted) at the bottom of the sidebar */
 .source-folders {
   border-top: 1px solid var(--grid-line);