fix(design): badge text clears AA — the ladder was painting a hue on a tint of itself (#3132)

Every status and priority badge used its raw hue as TEXT on a 12% tint of
that same hue. Measured on the dark palette, all six pairs failed the kit's
own AA floor: todo 1.60:1, in-progress 1.97:1, done 2.06:1, low 2.02:1,
high 2.92:1, medium 2.97:1, against 4.5. Four also failed in light mode.

The cause is structural, not a bad colour pick. A 12% tint sits near the
surface it composites over, so the hue as text on it has almost nowhere to
go. Strengthening the tint was measured and REJECTED: on a dark palette a
heavier tint moves the chip toward the light text and makes it worse. 12%
was already optimal.

So each pair gains a `-fg` sibling: the hue mixed toward --fs-text-primary
until it clears 4.5:1 worst-case over surface-raised AND surface-hover in
BOTH modes. Mixing toward that token rather than a literal is what makes one
declaration cover both — it inverts by mode, so the text follows.

Recorded in the DESIGN SYSTEM, not hand-written into theme.css: seven tokens
on design system 2, each carrying its measurement and its reasoning, then the
sheet regenerated. theme.css says not to hand-edit the --fs-* block and it is
right — a hand-edit would be silently reverted by the next regeneration.

The ladder keeps its shape. High priority still holds 52% saturation and
medium 31% — the rungs that need to shout still shout. Low, todo and done
wash toward neutral, which is what their own rationales ask for: status-todo
is derived from the border colour precisely so not-yet-started recedes.
Receding and illegible are different things and the old value was the second.

--fs-status-cancelled-fg was found by measuring, not by reasoning. Cancelled
derives from --fs-text-tertiary, which looks like the obviously-correct
"quiet" choice and is a HINT colour tuned for plain surfaces — 2.63:1 on a
badge tint in light mode.

StatusBadge additionally dropped a `color-mix(..., #000 15%)` that darkened
the hue: a light-mode instinct that made these worse on a near-black surface,
and a literal besides.

THE GUARD IS THE POINT. check_design_tokens.py now FAILS on any rule that
paints text with a token on a tint of that same token, and names the -fg
sibling as the fix. Verified by reintroducing the defect: exit 1 with it,
exit 0 without. Unlike a raw literal there is nothing to weigh up, so it
gates rather than reports.

Two `border-top-color` uses keep the raw hue, correctly — a border is a
non-text graphic and needs 3:1, which is what the hue is for.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

frontend/src/views/KnowledgeView.vue

@@ -946,10 +946,10 @@ onUnmounted(() => {
   border-radius: 8px;
   font-weight: 500;
 }
-.status--todo { background: var(--fs-status-todo-bg); color: var(--fs-status-todo); }
-.status--in_progress { background: var(--fs-status-in-progress-bg); color: var(--fs-status-in-progress); }
-.status--done { background: var(--fs-status-done-bg); color: var(--fs-status-done); }
-.status--cancelled { background: var(--fs-status-todo-bg); color: var(--fs-status-todo); text-decoration: line-through; }
+.status--todo { background: var(--fs-status-todo-bg); color: var(--fs-status-todo-fg); }
+.status--in_progress { background: var(--fs-status-in-progress-bg); color: var(--fs-status-in-progress-fg); }
+.status--done { background: var(--fs-status-done-bg); color: var(--fs-status-done-fg); }
+.status--cancelled { background: var(--fs-status-todo-bg); color: var(--fs-status-cancelled-fg); text-decoration: line-through; }
 
 .priority-badge {
   font-size: 0.7rem;
@@ -957,9 +957,9 @@ onUnmounted(() => {
   border-radius: 8px;
   font-weight: 500;
 }
-.priority--low { background: var(--fs-priority-low-bg); color: var(--fs-priority-low); }
-.priority--normal { background: var(--fs-priority-medium-bg); color: var(--fs-priority-medium); }
-.priority--high { background: var(--fs-priority-high-bg); color: var(--fs-priority-high); }
+.priority--low { background: var(--fs-priority-low-bg); color: var(--fs-priority-low-fg); }
+.priority--normal { background: var(--fs-priority-medium-bg); color: var(--fs-priority-medium-fg); }
+.priority--high { background: var(--fs-priority-high-bg); color: var(--fs-priority-high-fg); }
 
 .task-due {
   font-size: 0.78rem;