fix(ui): the palette ranks what you typed, and lib stops leaning on components

Typing "theme" put the channel "The Meltzone Podcast" (matched only through its handle
`@themeltzone`) above every "Theme: …" row, and Enter opened the channel — the palette listed
matches in pure group order and always highlighted the first one.

- CommandPalette ranks each word: label starts with it > elsewhere in the label > only the hint,
  keywords or group name; an item ranks by its worst word, then the sum. The group order stays
  fixed, rows are ranked inside each group, and the best row overall starts highlighted. The
  highlight is held by id and follows the best match until the arrows or the pointer pick a row,
  so a channel list landing mid-typing no longer shifts it.
- A11y: result groups are `role="group"` named by their heading; `aria-expanded` is false with
  nothing to choose; the listbox stays mounted (hidden) so `aria-controls` never names a missing
  element, and "Nothing matches" sits outside it; a polite status announces the count once the
  typing pauses.
- `Column`/`FilterMap`/`filterRows`/`isActive` move from `ui/tableHeader` to `lib/tableColumns`,
  and the player's auto/loop modes from `playerModalControls` to `lib/playerModes` — three lib
  helpers imported the column contract from a ui component, and `playerModalHooks` its types from a
  feature component.
- eslint: `lib/` may not import from `components/` at any depth, type-only and re-exports included;
  the boundary contract test proves it fires. CLAUDE.md and the ui README say so.
- keymap: `dispatch`'s docblock sat stacked on `matchesShortcut`'s; moved onto `dispatch`.

frontend/src/lib/keymap.ts

@@ -188,10 +188,6 @@ export function matches(e: KeyboardEvent, chord: string): boolean {
   return keyMatches(e, key);
 }
 
-/** Run `scope`'s map against an event. Returns true when a shortcut matched (the handler decides
- *  whether to `preventDefault`, because only it knows if it actually acted). `handlers` is a mapped
- *  type over the scope's ids, so the table and the implementation cannot drift without tsc saying
- *  so. Skipped while typing unless the row opts in with `allowInInput` (Escape, and only Escape). */
 /** Test an event against ONE row's chords, by id. The escape hatch for a `handledLocally` row: it is
  *  matched at the element level (Shift+F10 belongs to whichever row has focus, not to the window),
  *  but it must still go through `matches` or the table's `keys` become decoration. They had: the
@@ -210,6 +206,10 @@ export function matchesShortcut<S extends KeyScope>(
   return !!row?.keys.some((k) => matches(e, k));
 }
 
+/** Run `scope`'s map against an event. Returns true when a shortcut matched (the handler decides
+ *  whether to `preventDefault`, because only it knows if it actually acted). `handlers` is a mapped
+ *  type over the scope's ids, so the table and the implementation cannot drift without tsc saying
+ *  so. Skipped while typing unless the row opts in with `allowInInput` (Escape, and only Escape). */
 export function dispatch<S extends KeyScope>(
   e: KeyboardEvent,
   scope: S,