fix(a11y): make every text colour clear WCAG AA on every ramp

a11y.md flagged --yj-text-tertiary on --yj-bg-surface as 'borderline
(~4.1:1) but that needs a real measurement', and plan 007 parked it as
'worth measuring before planning'. Measured, against the rendered app
and then across all three background ramps: it failed AA in nine of
twelve text/surface combinations, as low as 2.31:1 on dark's overlay
and 2.55:1 on light's -- the app's most-used secondary text colour,
failing on every view. Not borderline. 110 failing nodes across twelve
views, now 0 of 659.

Three separate mechanisms, and only the first is the finding:

- The ramps. Tertiary is raised per ramp (#a6a6a6 dark, #949494 darker,
  #5c636a light), sized to the lightest surface it actually sits on and
  keeping its hue. Sizing it to bgOverlay too would need a grey lighter
  than secondary, so bgOverlay is documented as not a text surface and
  the one component that put text there uses primary.
- The avatar generator. hsl(hue, 45%, 35%) behind white initials failed
  for 35 of the 360 hues -- the yellow-green band -- so which artists
  were unreadable depended on how their names hashed. The two a sweep
  found were not the finding. 32% clears every hue.
- Jobs' local #ff6b6b, at 4.15:1 on elevated.

Pinned by a unit test over the palette table rather than a DOM sweep:
the ramps are pure data, and checking only what happens to be on screen
is exactly how the light ramp went unexamined. Note that make ui-visual
cannot see any of this -- the component tier renders the fallbacks,
because theme-store sets :root only in the real app.

frontend/src/components/jobs/job-details-drawer.ts

@@ -132,7 +132,7 @@ export class JobDetailsDrawer extends LitElement {
             }
 
             .stage.error {
-                color: #ff6b6b;
+                color: #ff8787;
             }
 
             .stage-count {
@@ -144,7 +144,7 @@ export class JobDetailsDrawer extends LitElement {
             .stage-error {
                 grid-column: 2 / -1;
                 font-size: var(--yj-text-sm);
-                color: #ff6b6b;
+                color: #ff8787;
                 overflow-wrap: anywhere;
             }
 

frontend/src/components/jobs/job-format.ts

@@ -154,7 +154,7 @@ export const jobStateStyles = css`
     }
 
     .tone-danger {
-        --job-tone: #ff6b6b;
+        --job-tone: #ff8787;
     }
 
     .tone-success {

frontend/src/components/jobs/job-indicator.ts

@@ -153,7 +153,7 @@ export class JobIndicator extends LitElement {
                 width: 6px;
                 height: 6px;
                 border-radius: 50%;
-                background: #ff6b6b;
+                background: #ff8787;
                 flex-shrink: 0;
             }
 

frontend/src/components/jobs/job-log-view.ts

@@ -132,7 +132,7 @@ export class JobLogView extends LitElement {
             }
 
             .entry.error .message {
-                color: #ff6b6b;
+                color: #ff8787;
             }
 
             .detail {

frontend/src/components/jobs/job-row.ts

@@ -180,7 +180,7 @@ export class JobRow extends LitElement {
             .error {
                 margin-top: 0.45em;
                 font-size: var(--yj-text-sm);
-                color: #ff6b6b;
+                color: #ff8787;
                 overflow-wrap: anywhere;
             }
 
@@ -214,7 +214,7 @@ export class JobRow extends LitElement {
             }
 
             button.danger:hover:not(:disabled) {
-                color: #ff6b6b;
+                color: #ff8787;
             }
 
             button:disabled {

frontend/src/components/jobs/jobs-view.ts

@@ -201,7 +201,7 @@ export class JobsView extends ViewLifecycleMixin(LitElement) {
             }
 
             button.action.danger {
-                color: #ff6b6b;
+                color: #ff8787;
                 border-color: rgba(255, 107, 107, 0.35);
             }