feat(web): session list one-list, hover card, row menus, rename, manual ordering

Sidebar session list grows the figma 239-10458 feature set and the
workspace/session browsing region moves wholesale into ui-workspace:

- Group-by menu (WorkSpace / In one list): flat mode lists every session
  top-level, strictly newest-first; the choice persists across reloads.
- Session rows get a 500ms hover detail card (title / relative time /
  status line) and a ... menu (Rename / Fork session / Delete session,
  visual-only for now); workspace headers get ... with Rename (wired) and
  Delete workspace (visual-only).
- workspace.rename RPC: trims, rejects duplicate titles on the create
  chain (workspace-name-conflict), no-op on same title; modal dialog with
  client-side duplicate pre-check.
- workspace.insertSessionBefore RPC (DOM-insertBefore semantics, omitted
  anchor appends): HTML5 drag reorder of root sessions inside a workspace
  group; order truth stays host-side, the view refreshes from the
  response/changed frame.
- Activity pinning removed: the session/event touchSession chain is gone;
  workspace accounts are manually owned (new sessions prepend, explicit
  reordering only). Contracts and tests updated, api catalog regenerated.
- ui-sidebar reduced to the column shell (brand, fold state machine, New
  Session, Settings) exposing one sidebar.workspaces hole with a two-fact
  owner share {wide, expandSidebar}; ui-workspace owns the whole region
  (header, search, grouped/flat lists, dialogs, drag) plus the picker via
  a shared WorkspaceCreateFlow. The old sidebar.workspace picker slot and
  its deferral indirection are gone.
- ui-primitives: Menu gains label entries, danger rows, and
  closeOnPointerLeave; new HoverCard (portaled, open-delay, disabled
  guard). Hover card and row menu never coexist.

packages/client/ui-primitives/src/HoverCard.tsx

@@ -0,0 +1,109 @@
+// HoverCard: delayed hover-preview card portaled to document.body.
+// Same portal mechanics as Menu: the wrapper span supplies the anchor rect,
+// the card is fixed-positioned at its right edge and repositions on
+// scroll/resize while open. Display-only — the card ignores pointer events
+// and closes the instant the pointer leaves the anchor (no close delay).
+
+import { useEffect, useLayoutEffect, useRef, useState } from 'react'
+import type { CSSProperties, ReactNode } from 'react'
+import { createPortal } from 'react-dom'
+import css from './HoverCard.module.css'
+
+/**
+ * Render an anchor with a hover-triggered preview card.
+ * @param props.anchor - the hover target (rendered in place inside a wrapper span).
+ * @param props.content - card content (display-only, no pointer interaction).
+ * @param props.openDelayMs - hover dwell before the card shows (default 500).
+ * @param props.disabled - suppress opening; turning true closes an open card.
+ * @returns anchor wrapper with the conditional portaled card.
+ */
+export function HoverCard({ anchor, content, openDelayMs = 500, disabled = false }: {
+  anchor: ReactNode
+  content: ReactNode
+  openDelayMs?: number
+  disabled?: boolean
+}) {
+  const rootRef = useRef<HTMLSpanElement>(null)
+  const cardRef = useRef<HTMLDivElement>(null)
+  const timerRef = useRef<ReturnType<typeof setTimeout> | null>(null)
+  const [open, setOpen] = useState(false)
+  const [pos, setPos] = useState<CSSProperties | null>(null)
+
+  const clearTimer = () => {
+    if (timerRef.current !== null) {
+      clearTimeout(timerRef.current)
+      timerRef.current = null
+    }
+  }
+
+  // Owner disabling mid-hover (menu opened, drag started) closes immediately.
+  useEffect(() => {
+    if (!disabled) return
+    clearTimer()
+    setOpen(false)
+  }, [disabled])
+
+  useEffect(() => clearTimer, [])
+
+  // Fixed-position from the anchor rect before paint; track the anchor while
+  // open (capture-phase scroll catches nested panes), as in Menu portal mode.
+  useLayoutEffect(() => {
+    if (!open) { setPos(null); return }
+    const place = () => {
+      const r = rootRef.current?.getBoundingClientRect() ?? null
+      if (r === null) return
+      const h = cardRef.current?.offsetHeight ?? 0
+      const top = r.top + h > window.innerHeight - 8 ? window.innerHeight - h - 8 : r.top
+      setPos({ left: r.right + 8, top })
+    }
+    place()
+    window.addEventListener('scroll', place, true)
+    window.addEventListener('resize', place)
+    return () => {
+      window.removeEventListener('scroll', place, true)
+      window.removeEventListener('resize', place)
+    }
+  }, [open])
+
+  // The first placement ran before the card mounted (height read 0): once the
+  // card's real height is measurable, correct the bottom-edge clamp.
+  useLayoutEffect(() => {
+    if (!open || pos === null || typeof pos.top !== 'number') return
+    const h = cardRef.current?.offsetHeight ?? 0
+    if (pos.top + h > window.innerHeight - 8) {
+      const top = window.innerHeight - h - 8
+      if (pos.top !== top) setPos({ ...pos, top })
+    }
+  }, [open, pos])
+
+  const card = open && pos !== null && (
+    <div ref={cardRef} className={css.card} style={pos}>
+      {content}
+    </div>
+  )
+
+  return (
+    <span
+      ref={rootRef}
+      className={css.root}
+      onPointerEnter={() => {
+        if (disabled) return
+        clearTimer()
+        timerRef.current = setTimeout(() => { setOpen(true) }, openDelayMs)
+      }}
+      onPointerLeave={() => {
+        clearTimer()
+        setOpen(false)
+      }}
+      // Any press inside the anchor (row click, menu trigger) dismisses the
+      // card immediately, without waiting for the owner to flip `disabled`.
+      onPointerDownCapture={() => {
+        clearTimer()
+        setOpen(false)
+      }}
+    >
+      {anchor}
+      {card !== false && createPortal(card, document.body)}
+    </span>
+  )
+}