feat(maestro): rename a session from the web sidebar

Right-clicking a card opens a custom context menu (rename, spawn similar,
kill). Rename swaps the name for an inline field; Enter commits, Escape and
blur cancel. The tree stops rebuilding while the field is open, so a catalog
delta cannot replace what is being typed into.

Refs #125

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

web/src/styles.css

@@ -814,6 +814,68 @@ textarea {
   white-space: nowrap;
 }
 
+/* Inline rename field (#125): sits exactly where the name it replaces did, so
+   the card does not jump when the edit starts. */
+input.leaf-rename {
+  font: inherit;
+  font-weight: 500;
+  font-size: var(--fs-13);
+  color: var(--ink);
+  background: var(--surface-2);
+  border: 1px solid var(--accent-ring);
+  border-radius: var(--r-2);
+  padding: 0 var(--sp-1);
+  min-width: 0;
+}
+
+input.leaf-rename:focus {
+  outline: none;
+  box-shadow: 0 0 0 3px var(--accent-tint);
+}
+
+/* Right-click menu on a session card (#125). Positioned from the click point,
+   so it is fixed to the viewport rather than to the scrolling sidebar. */
+.context-menu {
+  position: fixed;
+  z-index: var(--z-modal);
+  display: flex;
+  flex-direction: column;
+  min-width: 168px;
+  padding: var(--sp-1);
+  background: var(--surface-2);
+  border: 1px solid var(--border-strong);
+  border-radius: var(--r-3);
+  box-shadow: var(--shadow-2);
+}
+
+.context-menu-item {
+  appearance: none;
+  background: none;
+  border: 0;
+  border-radius: var(--r-2);
+  color: var(--ink);
+  font: inherit;
+  font-size: var(--fs-13);
+  text-align: left;
+  padding: var(--sp-1) var(--sp-2);
+  cursor: pointer;
+}
+
+.context-menu-item:hover,
+.context-menu-item:focus-visible {
+  background: var(--surface-3);
+  outline: none;
+}
+
+.context-menu-item.is-danger {
+  color: var(--danger);
+}
+
+.context-menu-item.is-danger:hover,
+.context-menu-item.is-danger:focus-visible {
+  background: var(--danger-tint);
+}
+
 /* Line 2 — dot + duration in the state's colour, then muted fragments. The
    state word itself is never spelled out here; the colour carries it. */
 .card-line2 {