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>

web/src/events.ts

@@ -50,7 +50,9 @@ function connect(){
     else if(ev.ev==='download_error'){
       const bar=document.querySelector(`.dlbar[data-bar="${ev.enclosure}"]`);
       if(bar) bar.classList.remove('live');
-      toast('Download failed: '+ev.msg,true); refreshEntries();
+      // Which item, and what to do: the reason (ev.msg) is in the daemon's log (#304).
+      const e=S.entries.find(x=>x.enclosures.some(n=>n.id===ev.enclosure));
+      toast(`Unable to download ${e?`"${entryName(e).text}"`:'a file'}. Try again with its download button.`,true); refreshEntries();
     }
     // Jev picked items out for someone's Signals: theirs are fetched again, and the one open.
     else if(ev.ev==='signal_hits'){