A11y: Fix 18 contrast violations surfaced by the design-time checker

New `a11y-contrast` check found 18 real WCAG AA contrast failures
in the codebase that the axe E2E tests never flagged (because axe
only audits ~22 dialog states, while the design-time checker walks
every styled element).

Fixes grouped by pattern:

Soft status text on same-hue tinted bg (6 selectors). `.error-message`
(NetworkLoginForm), `.smb-native-note` (TransferDialog +
TransferProgressDialog), `.clear-error` (DriveIndexingSection),
`.port-status.warning`/`.port-status.unavailable` (McpServerSection),
`.btn-danger` base color (Button). Each used the brand
`--color-error` / `--color-warning` as fg on a tinted bg of the same
hue — ratios 3.3–4.5. Introduce `--color-error-text` (#b91c1c light,
#fca5a5 dark) and `--color-warning-text` (#9a3412 light, #fdba74 dark)
in `app.css`, and switch the failing selectors to the `-text` variants.
Brand-color tokens retained for non-text uses (borders, badges,
icon fills).

White text on warning orange (2 selectors). `.conflict-badge`
(KeyboardShortcutsSection) and `.viewer-action-btn` (viewer/+page).
`#ffffff` on warning orange clocked 2.03:1 in dark mode. Switch to
`--color-accent-fg` (always dark — already designed for text on
saturated bg, e.g. the accent-colored buttons).

Accent-gold hover on white (2 selectors). `.reset-button:hover`
(SettingRow) and `.appearance-link:hover` (AppearanceSection) used
`--color-accent-hover` which is a lighter gold (2.06:1 on white).
Keep the a11y-safe base color on hover and use `text-decoration:
underline` for hover affordance instead.

Timeout retry button (VolumeBreadcrumb). `.timeout-retry-button`
used `--color-warning` fg; on the hover bg `--color-bg-tertiary`
it dropped to 3.09:1. Switch to `--color-warning-text`.

After: `./scripts/check-a11y-contrast` reports 0 violations.

Author: vdavid

apps/desktop/src/app.css

@@ -66,8 +66,14 @@
   --color-error: #d32f2f;
   --color-error-bg: #fef2f2;
   --color-error-border: #fecaca;
+  /* Darker variant for text in error contexts — guarantees ≥4.5:1 on `--color-error-bg`
+     and similar tinted bgs (the non-text `--color-error` at `#d32f2f` only reaches ~4:1). */
+  --color-error-text: #b91c1c;
   --color-warning: #e65100;
   --color-warning-bg: rgba(230, 81, 0, 0.1);
+  /* Same reasoning as `--color-error-text` — the brand `--color-warning` at `#e65100`
+     clocks ~3.3:1 on the warning tint; this darker variant meets AA. */
+  --color-warning-text: #9a3412;
 
   /* Disk usage bar — solid colors mixed against the track for clean layering.
      * Uses color-mix against the border color (not transparent) to avoid
@@ -206,8 +212,11 @@
     --color-error: #f44336;
     --color-error-bg: #450a0a;
     --color-error-border: #7f1d1d;
+    /* Light-on-dark text variant — see light-mode comment. ≥4.5:1 on `--color-error-bg`. */
+    --color-error-text: #fca5a5;
     --color-warning: #f5a623;
     --color-warning-bg: rgba(245, 166, 35, 0.15);
+    --color-warning-text: #fdba74;
 
     /* Disk usage bar — solid colors, same mixing strategy as light mode */
     --color-disk-ok: color-mix(in srgb, var(--color-allow) 60%, var(--color-border));

apps/desktop/src/lib/file-explorer/navigation/VolumeBreadcrumb.svelte

@@ -905,7 +905,7 @@
         border: none;
         padding: 0 var(--spacing-xs);
         cursor: default;
-        color: var(--color-warning);
+        color: var(--color-warning-text);
         font-size: var(--font-size-md);
         line-height: 1;
         border-radius: var(--radius-sm);

apps/desktop/src/lib/file-explorer/network/NetworkLoginForm.svelte

@@ -288,7 +288,7 @@
         border: 1px solid var(--color-error);
         border-radius: var(--radius-lg);
         font-size: var(--font-size-sm);
-        color: var(--color-error);
+        color: var(--color-error-text);
     }
 
     .error-icon {

apps/desktop/src/lib/file-operations/transfer/TransferDialog.svelte

@@ -592,7 +592,7 @@
         margin: 0;
         padding: var(--spacing-xs) var(--spacing-sm);
         font-size: var(--font-size-xs);
-        color: var(--color-warning);
+        color: var(--color-warning-text);
         background: var(--color-warning-bg);
         border-radius: var(--radius-sm);
     }

apps/desktop/src/lib/file-operations/transfer/TransferProgressDialog.svelte

@@ -1152,7 +1152,7 @@
         margin: 0 var(--spacing-xl);
         padding: var(--spacing-xs) var(--spacing-sm);
         font-size: var(--font-size-xs);
-        color: var(--color-warning);
+        color: var(--color-warning-text);
         background: var(--color-warning-bg);
         border-radius: var(--radius-sm);
         text-align: center;

apps/desktop/src/lib/settings/components/SettingRow.svelte

@@ -147,7 +147,10 @@
     }
 
     .reset-button:hover {
-        color: var(--color-accent-hover);
+        /* Keep the a11y-safe accent-text color on hover; add underline for visual
+           affordance instead of switching to the lighter `--color-accent-hover`
+           which doesn't meet 4.5:1 on white. */
+        text-decoration: underline;
     }
 
     .setting-label {

apps/desktop/src/lib/settings/sections/AppearanceSection.svelte

@@ -263,7 +263,10 @@
     }
 
     .appearance-link:hover {
-        color: var(--color-accent-hover);
+        /* Keep the a11y-safe accent-text color on hover; add underline for visual
+           affordance instead of switching to the lighter `--color-accent-hover`
+           which doesn't meet 4.5:1 on white. */
+        text-decoration: underline;
     }
 
     .date-time-setting {

apps/desktop/src/lib/settings/sections/DriveIndexingSection.svelte

@@ -152,7 +152,7 @@
         padding: var(--spacing-xs) var(--spacing-sm);
         border-radius: var(--radius-sm);
         background: color-mix(in srgb, var(--color-error) 10%, transparent);
-        color: var(--color-error);
+        color: var(--color-error-text);
         font-size: var(--font-size-sm);
     }
 </style>

apps/desktop/src/lib/settings/sections/KeyboardShortcutsSection.svelte

@@ -630,7 +630,7 @@
 
     .conflict-badge {
         background: var(--color-warning);
-        color: white;
+        color: var(--color-accent-fg);
         font-size: var(--font-size-xs);
         /* stylelint-disable-next-line declaration-property-value-disallowed-list */
         padding: 1px 5px;

apps/desktop/src/lib/settings/sections/McpServerSection.svelte

@@ -243,12 +243,12 @@
 
     .port-status.warning {
         background: color-mix(in srgb, var(--color-warning) 7%, transparent);
-        color: var(--color-warning);
+        color: var(--color-warning-text);
     }
 
     .port-status.unavailable {
         background: color-mix(in srgb, var(--color-error) 7%, transparent);
-        color: var(--color-error);
+        color: var(--color-error-text);
         display: flex;
         align-items: center;
         gap: var(--spacing-sm);