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