Split save/Stash actions, follow links in-app via reader pipeline, tune scroll, fix title entities

- ReaderScreen: bookmark icon is now a purely local save (just flips isSaved,
  no network) -- Stash archiving is a separate explicit action (new cloud
  icon), since it's a heavier networked action the user should trigger on
  purpose rather than have bundled into "save." Verified via direct DB
  queries and (once I stopped misreading small screenshots) the icon
  updates immediately in-session for both actions.
- New ReaderWebView.kt: shared WebView factory for the dark reader palette
  and link handling, used by both ReaderScreen and the new LinkReaderScreen.
  Links tapped inside an article's WebView now open in a lightweight
  in-app reader (extracted via the same Readability pipeline, no DB
  persistence) instead of falling through to the system browser --
  recursive, so a chain of links stays in-app. Verified live: tapping a
  link mid-article navigated to a real extracted page with a working back
  stack.
- WebView scroll tuning: overscroll glow and scrollbars off, on both the
  article reader and the new link reader -- aimed at the reported "still a
  little choppy" scrolling on top of the previous reload-on-recompose fix.
- FeedParser: some feeds (kottke.org among them) double-encode titles --
  the XML parser resolves outer XML escaping, but leftover HTML entities
  like "“" were showing up literally in the title text. Titles are
  now run through a second HTML-entity decode pass. Verified: a kottke
  title that previously showed a literal “ now renders the actual
  curly quote.

All changes verified live on the emulator against the real 107-feed dataset.

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