fix(steamdeck): install the plugin runner + harden Deck pad typing + repair update.sh

- scripts/steamdeck/install.sh (§2b) + update.sh: build and install the
  scripting runner user-scoped (~/.local wrapper + pinned bun + bundle) —
  SteamOS's read-only /usr can't take the .deb layout, so the console's
  plugin store reported "the plugin runner isn't installed" on every
  SteamOS host. update.sh retrofits it onto existing installs.
- plugins.rs runner discovery: check the ~/.local layout after the /usr
  ones; mention the SteamOS path in the not-installed error.
- update.sh: define warn() — it was used but never defined, so under
  `set -e` the first warn aborted the update before services restarted.
- pf-client-core gamepad: a Steam Input virtual pad forwarded on a real
  Deck (the only-pad case) now declares the DECK kind in its per-pad
  arrival instead of the wrapper's Xbox 360 identity — the session-level
  auto_pref already resolved SteamDeck, but the arrival overrides it on
  current hosts.
- reject tests: cover SetupFailed; move the foreign-code probe off 0x68.

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

crates/punktfunk-core/src/reject.rs

@@ -146,7 +146,7 @@ impl std::fmt::Display for RejectReason {
 mod tests {
     use super::*;
 
-    const ALL: [RejectReason; 9] = [
+    const ALL: [RejectReason; 10] = [
         RejectReason::PairingNotArmed,
         RejectReason::PairingBoundToOtherDevice,
         RejectReason::PairingRateLimited,
@@ -156,6 +156,7 @@ mod tests {
         RejectReason::Superseded,
         RejectReason::WireVersionMismatch,
         RejectReason::Busy,
+        RejectReason::SetupFailed,
     ];
 
     #[test]
@@ -177,7 +178,7 @@ mod tests {
     fn foreign_codes_stay_untyped() {
         // Bare closes, the client's own pair-done codes, and the deliberate-end codes must
         // never read as a host rejection.
-        for code in [0u32, 1, 0x41, 0x51, 0x52, 0x5f, 0x68, u32::MAX] {
+        for code in [0u32, 1, 0x41, 0x51, 0x52, 0x5f, 0x69, u32::MAX] {
             assert_eq!(RejectReason::from_close_code(code), None);
         }
     }