Keyboard shortcuts, after Feedly's

j/n and k/p step through the items, Shift-J and Shift-K through the feed
list, and g with a letter goes to a place: All Subscriptions, Directory,
Popular, Currently Listening, Settings. o plays the selected item, m marks
it read or unread and s keeps it, each by pressing the toolbar's own
button; v opens the original, Shift-A marks all read, r refreshes, [ hides
the feed list, and ? lists them all. None fire while typing, with a
modifier held, or with a dialog open.

Closes #8.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/page-smoke.js

@@ -91,6 +91,7 @@ const drive = [
   ['selectFeed (currently listening)', () => ctx.selectFeed(':listening')],
   ['selectFeed (all subscriptions)', () => ctx.selectFeed(':all')],
   ['logsModal', () => ctx.logsModal()],
+  ['keysModal', () => ctx.keysModal()],
   // `const S` is not reachable from here: top-level const/let do not become properties
   // of a vm context the way var and function declarations do.
   ['renderGroup', () => ctx.renderGroup(feed, [{ ...feed, id: 'child', group: 'f', orphaned: true }])],