fix(design): text on a tint of itself now clears AA app-wide, and the check gates it (#3141)

The badge fix (#3132) exposed the same defect everywhere: 48 rules painting a
token as TEXT on an inline color-mix tint of that same token. Worst raw
measurements, across every tint strength in use, both modes, over
page/raised/hover:

  accent 1.53:1 · success 1.67:1 · text-tertiary 2.15:1
  warning 2.32:1 · error 2.36:1                        against AA's 4.5

THE DEFECT IS IN THE HOUSE, NOT IN SCRIBE. The semantic hues are shared
family-wide, and the accent case was measured against every app's real
accent, not assumed from Scribe's: Minstrel 1.81, Forge 1.87, Steward 1.65,
Roundtable 3.01 — all failing. So the six -fg tokens are recorded on
FabledSword (design system 1), where their parents live, rather than copied
into each app.

45% toward --fs-text-primary clears AA for ALL FIVE accents (4.56-5.00), so
this is one house token rather than five overrides, and it keeps deriving
from --fs-accent — an app that overrides its accent still gets a legible
tinted-text colour in its own colour, the same mechanism as
--fs-accent-soft. The tokens are additive: a sibling app is unaffected until
it regenerates its own stylesheet.

One token is honestly redundant. --fs-text-secondary already passes at
4.82:1, and --fs-text-secondary-fg barely moves it. It exists so the rule
has NO exceptions, because the alternative is a permanent allow-list entry
for the one case that happens to pass — and a guard with an invisible
exception is a guard that erodes.

46 substitutions across 18 files, each rewriting only the `color:` inside a
block that tints its own background.

THE CHECK NOW GATES BOTH SPELLINGS. It previously reported the inline form,
because a gate nobody can satisfy on the day it lands gets switched off.
Both are clean, so both fail the build now.

And the check had a false-positive bug worth naming: its `color\s*:` regex
matched the tail of `border-color`, `border-left-color` and `outline-color`,
so it flagged seven rules that were already correct. A border is a non-text
graphic with a 3:1 floor, not text at 4.5. A check that cries wolf on
correct code is one that gets muted, so that mattered more than the noise.

Verified by construction, not by passing: reintroduced each defect form
(exit 1 each), and confirmed a legitimate border-only rule still exits 0.

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

frontend/src/assets/theme.css

@@ -31,6 +31,7 @@
   --fs-accent-faint: color-mix(in srgb, var(--fs-accent) 8%, transparent);  /* The faintest accent wash */
   --fs-accent-deep: color-mix(in srgb, var(--fs-accent) 70%, black);  /* The accent, darkened */
   --fs-accent-wash: color-mix(in srgb, var(--fs-accent) 22%, transparent);  /* Heaviest accent tint */
+  --fs-accent-fg: color-mix(in srgb, var(--fs-accent) 45%, var(--fs-text-primary));  /* Accent TEXT on an accent tint */
   --fs-gradient-cta: linear-gradient(135deg, var(--fs-accent), var(--fs-accent-deep));
   --fs-glow-cta: 0 2px 10px color-mix(in srgb, var(--fs-accent) 35%, transparent);
   --fs-glow-cta-hover: 0 4px 24px color-mix(in srgb, var(--fs-accent) 65%, transparent);
@@ -102,8 +103,11 @@
 
   /* semantic */
   --fs-success: var(--fs-action-primary);
+  --fs-success-fg: color-mix(in srgb, var(--fs-success) 45%, var(--fs-text-primary));  /* Success TEXT on a success tint */
   --fs-warning: #8B6F1E;
+  --fs-warning-fg: color-mix(in srgb, var(--fs-warning) 50%, var(--fs-text-primary));  /* Warning TEXT on a warning tint */
   --fs-error: #C04A1F;
+  --fs-error-fg: color-mix(in srgb, var(--fs-error) 50%, var(--fs-text-primary));  /* Error TEXT on an error tint */
   --fs-info: #3D5A6E;
   --fs-destructive: #6B2118;  /* irreversible — deliberately not the error colour */
 
@@ -148,7 +152,9 @@
   /* text */
   --fs-text-primary: #E8E4D8;  /* body, headings, labels — inverts by mode */
   --fs-text-secondary: #C2BFB4;
+  --fs-text-secondary-fg: color-mix(in srgb, var(--fs-text-secondary) 90%, var(--fs-text-primary));  /* Secondary TEXT on a secondary tint (barely moves; no exceptions) */
   --fs-text-tertiary: #9C9A92;
+  --fs-text-tertiary-fg: color-mix(in srgb, var(--fs-text-tertiary) 55%, var(--fs-text-primary));  /* Tertiary TEXT on a tertiary tint */
   --fs-text-on-action: #E8E4D8;  /* text on a filled colour — NOT mode-dependent */
 
   /* type */