Redesign Gant charts and fix issues

[ArtyomSavchenko]

Refresh the Gantt toolbar and timeline, including a dedicated View menu for grouping and colors. Align task rows and dates, improve navigation and empty-date states, and use the application locale for date labels.
Before:

After:

[ArtyomSavchenko]

Hi @MichaelUray
Please take a look if you have free time.

[MichaelUray]

Looked through it. The sidebar virtualization via row.y is a nice fix (no more drift after group headers), and the locale plumbing into createTimeScale is clean and tested. The gantt and tracker-resources gantt suites pass locally on this branch.

A few things before merge:

1. svelte-check is red for tracker-resources (and therefore github-resources): three errors from removed casts, in GanttView.svelte (setSpace(space)) and SubIssueSelector.svelte ($lookup on the status). Details inline. develop is green there.
2. Saved views with a fixed time window: navigationOffsetDays shifts the window, but a saved view only stores panAnchorDate, so an anchor saved beyond the base range is clamped on restore.
3. showIssueCode default: now visible by default, while the Customize View option still declares defaultValue: false.
4. Due-only issues: computeDateRange includes them, scheduledDates (Jump to start/end) doesn't, so the canvas can extend to an issue that the jump buttons can't reach.
5. Localization: the new visible strings are English in all non-English locales except Russian.
6. Minor: GanttZoomLabel isn't registered in ariaLabelKeys, so the zoom group gets an empty aria-label.

Happy to help with any of these. #11060 (working-day snapping for drags) touches GanttView.svelte too, but in disjoint hunks; both merge cleanly in either order.

[ArtyomSavchenko]

Hi @MichaelUray
Thank you for the review, I pushed corresponding fixes.