v2.17.0 - UI uplift (tokens + chip sheet + board) + Habits v2

Added

• Design-token foundation - all colors now come from semantic CSS variables (surface, text, border, accent, success/warning/danger), so the look is consistent and a dark theme later is a drop-in. Focus rings are unified to one accent color (an accessibility improvement).
• Chip-driven task sheet - adding and editing a task now happens in one sheet (a centered dialog on desktop, a keyboard-aware bottom-sheet on mobile). The title is a quick-add field (type friday #Work @urgent p1 / !urgent); recognized bits highlight and become chips you can adjust, Escape (or tapping a highlight on mobile) turns a recognized bit back into plain text, and #project / @label auto-create. Replaces the old inline add form + edit modal.
• Board view - a List | Board toggle with a Group-by control (due bucket / project / priority). The board shows horizontally-scrollable columns of rich cards (shadow, due-colour tint, priority pill). Each view remembers its own layout.
• Habits, reworked - a habit is now never completed/closed; its control is a daily check-in (an amber ring that fills green when done today). Habit rows are marked with a flame, a right-side Habits panel (and a mobile drawer) let you check in without leaving your task list, and a habit can carry a schedule (e.g. "every Tue & Thu") - the streak counts only the scheduled days, the dot row shows only those days, and off-days read "not due today." Checking in moves the habit out of the day's list.

Fixed

• A habit could previously be "completed" from the task list (closing it) while still showing on the Habits page - two disconnected "done" states. Habits are no longer completable; daily check-in is the only "done."

Notes

• Frontend-only; no database migration. The "x times a week" habit frequency model + decoupling deadline from habit schedules are deferred to a later Habits v2 Step 2.