fix(tracker): Gantt cascade — do not pull a predecessor back when its due falls on a non-working day

[MichaelUray]

Follow-up to #10992 (Gantt chart), which introduced the scheduler code changed here.

Problem

With a working-days calendar (Mon–Fri), an FS chain can end up with a successor starting on its predecessor's last day.

Example (Mon–Fri, FS chain A → B → C):

• A Mon Oct 5 – Fri Oct 9, B Mon Oct 12 – Tue Oct 13, C Wed Oct 14 – Thu Oct 15
• Drag A to Sun Oct 11 – Thu Oct 15

Expected: B Fri 16 – Sat 17, C Mon 19 – Tue 20.
Actual: B Thu 15 – Fri 16 (overlaps A's last day), C Mon 19 – Tue 20.

Root cause

The reverse pass in simulateCascade decides whether to pull a predecessor by comparing fsReverseAnchor(successor) with the predecessor's due date. In working-days mode fsReverseAnchor is not the inverse of fsAnchor when the predecessor ends on a non-working day: fsAnchor(Sat 17) = Mon 19, but fsReverseAnchor(Mon 19) = Fri 16 < Sat 17. So C (already correctly placed on Mon 19) pulls B back by a day. B's own link to A is never re-checked, because A is the primary edit.

Legacy calendar-day mode is not affected: its forward and reverse anchors are exact inverses.

Fix

Before pulling, check the violation with the forward anchor, the same check the outgoing pass uses (fsAnchor/ssAnchor/ffAnchor/sfAnchor against the successor's start or due date). A predecessor is pulled only if the constraint is actually violated. How far it gets pulled is unchanged.

Tests

scheduler-cascade.test.ts:

• Working-days mode: the chain above (B Fri 16 – Sat 17, no pull-predecessor); a successor dropped on the first working day after a Saturday-ending predecessor gives no-cascade; a real violation (successor on the predecessor's Friday) still pulls the predecessor to Wed 14 – Thu 15.
• Legacy mode: forward/reverse anchors are exact inverses for all four relation kinds and several lags; a chain push never emits pull-predecessor; existing pull behaviour is unchanged.

All gantt suites in plugins/tracker-resources and packages/gantt pass.

Out of scope: snapping drags to working days, and working-day durations for cascaded successors.