feat(ui): sidebar redesign — project zones, grouping modes, full-page surfaces (#2480)

* checkpoint: flatten sidebar core (flat sessions, zones, single mode, folders flat)

* checkpoint: sidebar nav + scheduled/archive full-page surfaces, recent zone header

* checkpoint: worktrees management surface via project menu

* checkpoint: docs, i18n, validation for sidebar redesign

* checkpoint: unified row/zone geometry, recent backfill, tooltips everywhere, primary spinner

* checkpoint: branch icon marker, date moved to rich tooltip, recent back to pure time window

* checkpoint: PR state on branch markers + tooltip, no reserved right space, aligned show-more, instant tooltips

* checkpoint: reserve hover-action space so title text is not overlapped

* checkpoint: tighten hover-action reserve

* checkpoint: color-only unread emphasis to avoid title reflow

* checkpoint: drop new-subfolder action, folder actions overlay on hover

* checkpoint: fix sticky project headers (sticky on trigger div), stuck elevation

* checkpoint: full-bleed semibold zone headers, no top scroll fade

* checkpoint: headers without background tint (typography-only emphasis)

* checkpoint: recent header flush with scroll top (no pre-stick bump)

* checkpoint: shared tooltip provider with grouping (instant handoff between rows)

* checkpoint: blur pointer-click focus so hover chrome hides on mouse-leave

* checkpoint: tooltip closeDelay bridges inter-row gap

* checkpoint: nav above controls, merged view dropdown, project-scoped bulk selection, cross-worktree folders

* checkpoint: folder header tooltip with full path name

* checkpoint: true page surfaces (hidden chat, header title, close-on-select), multirun page, run-now jump, folders on top, controls row polish

* checkpoint: rename mode — dual-instance outside-click fix, no vertical shift

* checkpoint: session grouping mode toggle (by-worktree default, flat option)

* checkpoint: worktree header — hover padding reserve + delete worktree action

* checkpoint: frosted sticky header backing under desktop vibrancy

* checkpoint: align worktree sub-header with project header icon column

* checkpoint: restore worktree group DnD reorder; dense vibrancy header tint (Chromium mask+backdrop-filter)

* checkpoint: vibrancy — drop scroller mask so backdrop-filter samples rows (Chromium backdrop-root limitation)

* checkpoint: vibrancy headers use opaque sidebar tone (Electron transparent-window backdrop-filter bug)

* checkpoint: nav collapsed to one row (New session + surface icons), mirrors Add project row

* checkpoint: raise sticky zone headers above row action layers (z-20)

* checkpoint: New session as full-width CTA + single quiet toolbar row

* checkpoint: New session row back to quiet text form above the toolbar

* checkpoint: align toolbar left icon with New session icon column

* checkpoint: hoverless flat header controls (color-only hover states)

* checkpoint: sticky project headers toggle in view dropdown (default on)

* checkpoint: full-page surfaces adapted — archive directory filter panel, scheduled master-detail, multirun without duplicate title bar

* checkpoint: multirun joins mutually exclusive surface set

* checkpoint: surfaces leave via navigation only (no close/cancel buttons), robust close-on-new-session, drop dead MultiRunWindow

* checkpoint: no scheduled header description, aligned empty-worktree note, collapse/expand covers worktree groups

* checkpoint: overlay scrollbar above sticky zone headers

* checkpoint: archive delete icons reveal on hover with padding shift

* checkpoint: new worktrees surface at top of the worktree list

* checkpoint: no grab cursor on worktree headers

* checkpoint: worktrees page list-only with inline action, no worktrees in edit dialog, drop menu ellipsis

* checkpoint: worktrees page uses full content width

* checkpoint: worktrees header — 'in' instead of em dash, no description

* checkpoint: drop legacy OpenCode badge from worktree list, tooltip without OpenCode mention

* review: bound pr summary cache

packages/ui/src/index.css

@@ -680,7 +680,9 @@ html:not(.dark) .chat-scroll {
   inset: 0;
   pointer-events: none;
   transition: opacity 0.2s ease;
-  z-index: 10;
+  /* Above sticky zone headers (z-20) — the thumb must never dive under
+     a stuck sidebar header while scrolling. */
+  z-index: 30;
 }
 
 .overlay-scrollbar--dense,