Keyboard, screen reader and contrast fixes from the interface review (#298 #299 #300 #301 #302 #303 #304 #305 #306 #307 #308 #309)

Found reviewing the main window, its dialogs and the Directory in all 25 palettes (13 themes,
light and dark), in Playwright against the test daemon.

- #298: an item's title is a button, so Tab and a screen reader can open it; the feed list's
  rows, places, Signals and the Directory's shows are links to a screen reader (asLink), named
  by what they show, the open one aria-current. Not role=button, which would flatten a folder's
  triangle inside it.
- #299: .ep:focus-within shows the row's actions; Tab reached Play and Delete at opacity 0.
- #300: the read toggle is named Mark read / Mark unread, the dot hidden from screen readers.
- #301: the seek slider is named Position, its value read as "12:30 of 45:00".
- #302: ::placeholder in --faint; the browser's grey was 2.7-4.4:1 in 20 palettes. The search
  and filter boxes have names that do not depend on their placeholder.
- #303: #toasts is role=status; an error toast stays until dismissed, at most four at once.
- #304: api() says what to do when iPX cannot be reached or answers 500 (whose text is the
  daemon's internals, already in its log); play() failures are put in words and reported, an
  AbortError ignored; a failed download names its item.
- #305, #308: --field, the theme's --fg mixed into --bg in OKLab (--fieldmix, 60% and up to 80%
  for Catppuccin light), edges text boxes, selects, chips, the OPML box and switch tracks,
  phones included, and rings a light theme's switch knob. tests/contrast.js holds it to 3:1 on
  bg, panel, panel2 and raise in every palette. --line stays for rules. Fields lose outline:0,
  so they take the same focus ring as everything else.
- #306: openModal makes the card role=dialog aria-modal, labelled by its heading, focuses it,
  and makes the rest of the body inert until closeModal, which gives focus back to what opened
  it. Not <dialog>: its top layer would cover the toasts and their Dismiss.
- #307: the labels in Add a feed, Settings, Download latest and OPML point at their boxes.
- #309: Settings shows iPX's and the page's versions at its foot.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/contrast.js

@@ -11,6 +11,7 @@ const blocks = {};
 for (const m of css.matchAll(/^(:root(?:\[[^\]]+\])*)\s*\{([^}]*)\}/gm)) {
   const vars = {};
   for (const v of m[2].matchAll(/--(\w+):\s*(#[0-9a-f]{6})\b/gi)) vars[v[1]] = v[2].toLowerCase();
+  const mix = m[2].match(/--fieldmix:\s*(\d+)%/); if (mix) vars.fieldmix = +mix[1] / 100;
   if (Object.keys(vars).length) blocks[m[1]] = vars;
 }
 
@@ -49,6 +50,21 @@ for (const sel of Object.keys(blocks)) {
 }
 themes['modern'] = base;
 
+// --field, a text box's and a switch's edge, is --fg mixed into --bg in OKLab, as color-mix() does.
+const oklab = h => {
+  const [r, g, b] = [1, 3, 5].map(i => parseInt(h.slice(i, i + 2), 16) / 255).map(c => c <= .04045 ? c / 12.92 : ((c + .055) / 1.055) ** 2.4);
+  const [l, m, s] = [.4122214708 * r + .5363325363 * g + .0514459929 * b, .2119034982 * r + .6806995451 * g + .1073969566 * b, .0883024619 * r + .2817188376 * g + .6299787005 * b].map(Math.cbrt);
+  return [.2104542553 * l + .793617785 * m - .0040720468 * s, 1.9779984951 * l - 2.428592205 * m + .4505937099 * s, .0259040371 * l + .7827717662 * m - .808675766 * s];
+};
+const fromOklab = ([L, a, b]) => {
+  const [l, m, s] = [L + .3963377774 * a + .2158037573 * b, L - .1055613458 * a - .0638541728 * b, L - .0894841775 * a - 1.291485548 * b].map(x => x ** 3);
+  return '#' + [4.0767416621 * l - 3.3077115913 * m + .2309699292 * s, -1.2684380046 * l + 2.6097574011 * m - .3413193965 * s, -.0041960863 * l - .7034186147 * m + 1.707614701 * s]
+    .map(c => Math.min(1, Math.max(0, c)) <= .0031308 ? 12.92 * Math.max(0, c) : 1.055 * Math.min(1, c) ** (1 / 2.4) - .055)
+    .map(c => Math.round(c * 255).toString(16).padStart(2, '0')).join('');
+};
+for (const p of Object.values(themes)) { const f = oklab(p.fg), g = oklab(p.bg), k = p.fieldmix; p.field = fromOklab(f.map((v, i) => v * k + g[i] * (1 - k))); }
+RULES.push(['field', ['bg', 'panel', 'panel2', 'raise'], 3]);  // a text box's or a switch's edge, wherever one sits
+
 let bad = 0;
 for (const [name, p] of Object.entries(themes)) {
   for (const [fg, grounds, min] of RULES) for (const g of grounds) {