fix(hotkey): resolve physical-key codes; Super-as-modifier; surface backend registration errors

Three correctness fixes to the hotkey recorder based on dogfood logs:

1. Modifier set now includes Super / OS / Hyper (webkit2gtk on Linux
   fires e.key === "Super" for the Windows key — previously that key
   got captured as the final trigger, producing invalid 'Ctrl+Shift+Super'
   strings the evdev parser rejected).

2. resolveTriggerKey() uses e.code (physical, shift-independent key)
   to resolve shifted punctuation back to the unshifted name the evdev
   parser understands: '+' -> '=', '|' -> '\\', etc. Letters and digits
   also use e.code (KeyA -> A, Digit1 -> 1) to avoid layout quirks.

3. Numpad keys intentionally not mapped to main-keyboard equivalents —
   they are distinct evdev codes. Leaves the parser to reject them so
   the user gets a toast instead of a silently-wrong binding.

Registration failures now surface as a toast and revert
settings.globalHotkey to the last successfully-registered value (if
any), so the UI cannot lie about what is actually bound.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/routes/+layout.svelte

@@ -117,6 +117,17 @@
       }
     } catch (err) {
       console.error("Hotkey registration failed:", err);
+      const msg = err instanceof Error ? err.message : String(err);
+      toasts.error(
+        "Hotkey not registered",
+        `${hotkey} — ${msg}. Reverted to ${registeredHotkey ?? "previous value"}.`,
+      );
+      // Revert the in-memory setting to the last successfully-registered hotkey
+      // so the UI does not lie about what is actually bound.
+      if (registeredHotkey && registeredHotkey !== hotkey) {
+        settings.globalHotkey = registeredHotkey;
+        saveSettings();
+      }
     }
   }