fix(host/dualsense): report full battery + log rumble forwarding

Two DualSense (UHID) fixes surfaced live on the Bazzite host:

- Battery: serialize_state never set the input report's status byte (struct off 52 →
  r[53]), so hid-playstation read battery capacity 0 and SteamOS warned "low battery"
  even on a fully-charged pad. Set it to 0x0A (discharging, low nibble 0xA → 100 %) —
  a virtual pad has no real cell. (Forwarding the client pad's real charge is a later
  feature.) Regression assert added to the layout test.
- Rumble diagnostic: log the silent→active transition when forwarding a buzz on the
  0xCA plane, so a live test can tell "host never receives rumble from the game"
  (Steam Input / parse) apart from "client doesn't render it". Once per buzz, no spam.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/punktfunk-host/src/m3.rs

@@ -1254,6 +1254,11 @@ fn input_thread(
         pads.pump(
             |pad, low, high| {
                 if let Some(s) = rumble_state.get_mut(pad as usize) {
+                    // Log the silent→active transition (once per buzz) so a live test can tell
+                    // "host never gets rumble from the game" apart from "client doesn't render it".
+                    if *s == (0, 0) && (low != 0 || high != 0) {
+                        tracing::info!(pad, low, high, "rumble: forwarding to client (0xCA)");
+                    }
                     *s = (low, high);
                     rumble_seen[pad as usize] = true;
                 }