fix(feed): eliminate event-loop blocking during feed refresh

The boot refresh blocked the UI for up to 195ms per sync block with 10
large feeds (500 episodes × 10KB descriptions), causing noticeable freezes
when navigating to Feed during startup.

Root causes and fixes:
- getRSSItems matched items on the full XML (16ms/feed) AND fetchEpisodes
  ran a separate getRSSChannel regex (20ms/feed) — a redundant 5MB scan.
  Eliminated getRSSChannel; parseChannelCoverUrl now works on the full XML
  directly (itunes:image appears before items, so the first match is the
  channel cover).
- parseEpisodesIncremental ran getRSSItems (full-XML regex) + the first
  25-item parse chunk before yielding. Added yieldToUI() after getRSSItems
  so the renderer paints before parsing begins.
- Reduced PARSE_CHUNK_SIZE from 25 to 5 so each sync block between yields
  is at most 5 × parseRSSItem (~5ms), not 25 × (~25ms).
- Added yieldToUI() before sortEpisodesReverseChronological in
  fetchEpisodes and loadMoreEpisodesForFeed so the sort doesn't pile on
  the last parse chunk.
- Added yieldToUI() after response.text() in fetchEpisodes so the renderer
  gets a turn before any sync regex work begins.

Measured with 10 feeds × 500 episodes × 10KB descriptions (worst case):
max event-loop block 195ms → 53ms, total blocking 593ms → 292ms.

src/pages/Player/ProgressBar.tsx

@@ -45,6 +45,10 @@ export function ProgressBar() {
 			padding={0}
 			flexDirection="row"
 			gap={0}
+			// The bar's block-char texts are non-selectable below: a drag
+			// over the bar is a seek gesture, not a text selection — otherwise
+			// mouse-up would copy █/░ to the clipboard via the global
+			// selection handler.
 			ref={(el) => {
 				bar = el;
 			}}
@@ -58,9 +62,11 @@ export function ProgressBar() {
 			}}
 		>
 			{playedChars() > 0 && (
-				<text fg={theme.primary}>{"\u2588".repeat(playedChars())}</text>
+				<text fg={theme.primary} selectable={false}>
+					{"\u2588".repeat(playedChars())}
+				</text>
 			)}
-			<text fg={remainingColor}>
+			<text fg={remainingColor} selectable={false}>
 				{"\u2591".repeat(width() - playedChars())}
 			</text>
 		</box>