fix(ui): keep a touch-only affordance reachable, or absent

Three controls are revealed by :hover and are the only route to their
action on a device that has none. #68 hid the home card's play button on
touch, which was right because tapping the card does the same thing;
these are the opposite case, so hiding them removes the action outright
and leaving them costs the same long-press flash #68 was filed for --
they are visibility:hidden / opacity:0, so on touch they are invisible
controls that still take taps.

track-details' cover-art overlay and remove, and shortcut-capture's
reset, are always visible under `@media not all and (hover: hover)`.

The queue row's remove is the third case the report names and takes the
other treatment, because #60 has since landed: the row's context menu is
a bottom sheet carrying "Remove from Queue", so the action is one
long-press away and an always-visible X would spend part of a 424px row
on something already reachable. It is display:none outside
`(hover: hover) and (pointer: fine)` rather than visibility:hidden,
which would leave a button holding its hit area and its place in the
accessibility tree -- the trap this issue is about.

The rule is not extracted into styles/ yet: that leaves two call sites
of the always-visible form, under the four the report names.

No tier here can render as a touch device, so the tests read the parsed
stylesheet the way #68's does and say so; the touch and hover renderings
were measured against the running app in a hasTouch context instead.

Closes #137

frontend/test/components/hover-affordance.test.ts

@@ -1,5 +1,6 @@
 /**
- * A hover affordance is gated on the device having hover.
+ * A hover affordance is gated on the device having hover — in whichever
+ * direction keeps the action reachable.
  *
  * The home page's cover cards reveal a play button on :hover. A touch
  * long-press synthesises a hover state in the WebView, so on a phone
@@ -7,6 +8,15 @@
  * utils/long-press.ts is measuring for a context menu — a control
  * appearing because the user was reaching for a different one.
  *
+ * #137 is the same sweep with the opposite answer for two of its three
+ * cases. Where the revealed control is the *only* route to its action,
+ * hiding it removes the action, so it is always visible where there is
+ * no hover: `track-details`'s cover-art overlay and remove, and
+ * `shortcut-capture`'s reset. The queue's per-row remove is the third,
+ * and is the redundant kind — since #60 the row's context menu is a
+ * bottom sheet carrying "Remove from Queue" — so it takes #68's
+ * treatment here.
+ *
  * This is asserted against the *parsed stylesheet* rather than by
  * emulating a touch device, and that is a limitation worth stating
  * rather than hiding. CDP's Emulation.setEmulatedMedia does not reach
@@ -24,6 +34,9 @@
 import { describe, expect, it } from 'vitest';
 
 import '@components/home-view/home-view';
+import '@components/queue-panel/queue-panel';
+import '@components/track-details/track-details';
+import '@components/config-page/shortcut-capture';
 import { fixture } from '@test/support/render';
 
 /** Every rule in the element's own adopted stylesheets, flattened. */
@@ -83,3 +96,91 @@ describe('the home card play button', () => {
     expect(unconditional.some((r) => /display:\s*none/.test(r.text))).toBe(true);
   });
 });
+
+describe("the queue row's remove button", () => {
+  it('is absent where the device has no hover, the menu carrying the action', async () => {
+    const el = await fixture('queue-panel', {});
+    const rules = rulesOf(el);
+
+    expect(rules.length).toBeGreaterThan(0);
+
+    // visibility:hidden alone would leave an invisible button holding
+    // its hit area on a phone, which is the trap #68's commit names.
+    const unconditional = rules.filter(
+      (r) => r.condition === null && r.text.startsWith('.remove-button'),
+    );
+
+    expect(unconditional.length).toBeGreaterThan(0);
+    expect(unconditional.some((r) => /display:\s*none/.test(r.text))).toBe(true);
+
+    const reveals = rules.filter(
+      (r) =>
+        r.text.includes('.remove-button') && /visibility:\s*visible/.test(r.text),
+    );
+
+    expect(reveals.length).toBeGreaterThan(0);
+
+    for (const rule of reveals) {
+      expect(rule.condition).toMatch(/hover:\s*hover/);
+      expect(rule.condition).toMatch(/pointer:\s*fine/);
+    }
+  });
+});
+
+/**
+ * The two affordances that are the only route to their action.
+ *
+ * Asserted as "there is a rule showing it, and its condition is a
+ * *negated* hover query" — the same stylesheet reading as above, for
+ * the same reason: this tier's iframe cannot be emulated as a touch
+ * device, and the regression worth catching is someone folding the rule
+ * away as redundant on the desktop it does nothing on.
+ */
+describe('an affordance with no other route', () => {
+  const cases: Array<[string, string, string[]]> = [
+    ['track-details', 'track-details', ['.cover-art-overlay', '.cover-art-remove']],
+    ['shortcut-capture', 'shortcut-capture', ['.reset-btn']],
+  ];
+
+  for (const [name, tag, selectors] of cases) {
+    it(`${name} shows it where the device has no hover`, async () => {
+      const el = await fixture(tag, {});
+      const rules = rulesOf(el);
+
+      expect(rules.length).toBeGreaterThan(0);
+
+      for (const selector of selectors) {
+        const shown = rules.filter(
+          (r) =>
+            r.condition !== null &&
+            r.text.includes(selector) &&
+            /opacity:\s*1/.test(r.text),
+        );
+
+        const touch = shown.filter((r) => /not[\s\S]*hover:\s*hover/.test(r.condition!));
+
+        expect(touch.length).toBeGreaterThan(0);
+      }
+    });
+  }
+
+  // The one half this tier can measure rather than read: the query is
+  // negated, so on the hover-capable browser running these tests the
+  // control must still be revealed by hover and by nothing else. A rule
+  // written without the `not` would show it here, permanently, on every
+  // desktop.
+  it('leaves the desktop reveal alone, where the device does have hover', async () => {
+    expect(matchMedia('(hover: hover)').matches).toBe(true);
+
+    const el = await fixture('shortcut-capture', {
+      action: 'player.next',
+      label: 'Next Track',
+      currentKey: 'X',
+      defaultKey: 'N',
+    });
+    const btn = el.shadowRoot?.querySelector('.reset-btn');
+
+    expect(btn).not.toBeNull();
+    expect(getComputedStyle(btn!).opacity).toBe('0');
+  });
+});