feat(e10): put every keyboard shortcut in one table

Six surfaces each owned a private keydown listener with its own key
literals and its own idea of "am I typing?", and they had drifted:
PlexPlayer matched `case "a"` without checking modifiers, so Ctrl+A
(select all) cycled the audio track, and its typing guard missed
<select> and contentEditable where the other two surfaces covered both.

lib/keymap.ts is a TABLE, not a dispatcher. Each surface keeps its own
listener and closures - PlexPlayer's refs are not worth re-plumbing -
but the chords, the modifier rules and the typing guard live in one
place, and dispatch() binds a scope's rows to handlers through a mapped
type, so a row without a handler (or a handler without a row) is a tsc
error rather than a comment someone forgets.

Matching is now exact on modifiers, which is what kills the Ctrl+A bug
and lets Shift+arrow be its own row beside the bare arrow. Escape opts
out of the typing guard (allowInInput) so it stays the way out of a
player's own subtitle-offset field.

The player's shortcut sheet renders helpLines() instead of a hand-copied
array beside the handler - the two used to be edited separately, which
is how a sheet ends up documenting a key that no longer exists. Labels
move to the new `keys` i18n namespace (EN + HU), and a test asserts
every row is named in both.

frontend/src/components/PlexBrowse.tsx

@@ -39,6 +39,7 @@ import { usePlex, usePlexActions } from "./PlexProvider";
 import { usePublishPlexView } from "./PlexViewBridge";
 import { EpisodeCard, PlexPosterCard } from "./plexCards";
 import { PlexInfoView, PlexPersonView, PlexSeasonView, PlexShowView } from "./plexViews";
+import { dispatch } from "../lib/keymap";
 
 // Lazy: the rich player (pulls in hls.js) loads only when something is first played.
 const PlexPlayer = lazy(() => import("./PlexPlayer"));
@@ -163,31 +164,31 @@ export default function PlexBrowse() {
   }, [sub.view.kind]);
 
   // Backspace steps back one drill-down level (grid ← show ← season, and out of info/playlist),
-  // matching the browser/mouse Back. The player has its OWN Backspace handling, so we skip it here;
-  // and never hijack Backspace while typing in a field.
+  // matching the browser/mouse Back. The player has its OWN Backspace handling, so we skip it here
+  // (its "player" view kind is deliberately absent from the list below); the typing guard and the
+  // chord itself come from the shared keymap.
   useEffect(() => {
     const onKey = (e: KeyboardEvent) => {
-      if (e.key !== "Backspace") return;
-      const el = document.activeElement as HTMLElement | null;
-      const tag = (el?.tagName || "").toLowerCase();
-      if (tag === "input" || tag === "textarea" || tag === "select" || el?.isContentEditable)
-        return;
-      if (
-        [
-          "grid",
-          "playlists",
-          "collections",
-          "show",
-          "season",
-          "info",
-          "person",
-          "playlist",
-          "collection",
-        ].includes(sub.view.kind)
-      ) {
-        e.preventDefault();
-        sub.back();
-      }
+      dispatch(e, "plexBrowse", {
+        back: (ev) => {
+          if (
+            ![
+              "grid",
+              "playlists",
+              "collections",
+              "show",
+              "season",
+              "info",
+              "person",
+              "playlist",
+              "collection",
+            ].includes(sub.view.kind)
+          )
+            return;
+          ev.preventDefault();
+          sub.back();
+        },
+      });
     };
     window.addEventListener("keydown", onKey);
     return () => window.removeEventListener("keydown", onKey);