plugin-gantt: auto-schedule ignores self-dated summaries & writes without confirming; export draws phantom group bars, no in-bar titles, opaque filenames; charts render in the viewer's time zone #2682

Follow-up batch to #2676 / #2677, all reproduced live on the 4-level 排班计划 tree (project/product groups → self-dated summary plans → locked dispatch leaves).

1. Reschedule skips every parent task — and the toolbar wand writes without asking

computeProjectReschedule treats EVERY parent as a derived rollup (if (summaries.has(id)) continue), so under summaryExtent: 'self' a plan that has dispatch children is silently immune to auto-schedule and to the post-drag conflict cascade — the scheduling twin of the editability gap fixed in #2677. Also the toolbar auto-schedule button commits the bulk reschedule immediately, while the drag-conflict path already asks first ("Auto-reschedule N affected tasks?") — an in-component inconsistency for the more impactful action. And pushed starts don't snap to shift-band boundaries (班次边界), so a successor can be scheduled mid-band.

2. Export defects (导出内容异常 + 文件名)

• PNG/PDF export draws a rollup bar for every parent row including pure grouping levels (type 'group' — 项目/产品) that the live chart renders bar-less → phantom full-span bars.
• Bars export as bare color blocks: no in-bar titles (live chart shows 计划名 on summaries, executor on leaves).
• Filenames are an opaque gantt-week.png — no business context, repeated exports overwrite each other.

3. Charts render in the viewer's browser time zone (班次错位)

All calendar math — shift bands, day columns, drag snapping, today line, date labels — uses the viewer's local zone. A plan starting 7/20 08:00 Beijing displays as "7/19 evening" in a UTC-7 browser, bands misalign, and drags land on misaligned instants. Business shifts are a wall-clock fact of one zone; the chart needs a project time zone (MS Project model).

Fix direction (PR follows)

• computeProjectRescheduleDetailed: self-extent own-dates summaries shift like tasks and carry their unlocked subtree (group-drag semantics, 顺延-only max rule); locked violators reported as skipped; snapStart hook for band snapping; back-compat wrapper.
• Toolbar wand: compute → confirm dialog ("shift N task(s)? M locked skipped") → apply; transient notice when clean.
• Export: skip group rows, draw ellipsis-truncated in-bar titles (CJK-aware width), filenames <gantt.exportFileName|object label|API name>-<yyyyMMdd-HHmm>.<ext>.
• New gantt.timeZone (IANA): shifted-clock shim renders the configured zone's wall time for every viewer; writes translate back to real instants; DST-safe; omitted = unchanged.