feat(rumble): host-authoritative self-terminating envelopes (0xCA v2)

Rumble was level-triggered, unbounded state on a lossy channel: a non-zero
level meant "buzz until further notice", healed only by the host re-sending
state every 500 ms, and every client guessed when the host had died with its own
magic timeout (SDL 1.5 s, Apple 1.6 s, Android up to 60 s). A lost stop, a
reordered start, or a dead host could drone the motor for seconds.

Make "stuck rumble" inexpressible on the wire. The 0xCA datagram grows a
length-tolerant tail — [u8 seq][u16 ttl_ms] — so it self-terminates: the host
authorizes a level for at most ttl_ms and renews it (~120 ms) while it holds,
letting an abandoned one lapse client-side. seq is a per-pad wrapping reorder
gate (reusing GamepadSnapshot::seq_newer) so a reordered stale start can't
re-light a stopped motor. Decoders read the first 7 bytes as a plain level and
ignore the tail, so no wire-version bump: an old client renders a new host's
levels, and a new client falls back to its prior staleness heuristic against an
old host (ttl = None). All four generation pairings render correctly.

- core: encode_rumble_datagram_v2 / decode_rumble_envelope (datagram.rs); the
  client demux applies the seq gate then forwards (pad, low, high, Option<ttl>);
  next_rumble is unchanged (drops ttl), next_rumble_ttl keeps it; ABI adds
  punktfunk_connection_next_rumble2 + PUNKTFUNK_RUMBLE_NO_TTL, ABI_VERSION 4->5
  (WIRE_VERSION unchanged — the tail is backward-compatible).
- host (punktfunk1.rs): the flat 500 ms refresh becomes a renewal loop that bumps
  seq + stamps a fresh TTL on active pads and drains a short post-stop zero burst,
  then goes quiet. Hatches: PUNKTFUNK_RUMBLE_ENVELOPE=0 (legacy v1 + flat refresh,
  a bisect switch), PUNKTFUNK_RUMBLE_TTL_MS (clamped [150, 5000]).
- renderers honor the TTL as their playback duration/deadline and keep their old
  heuristic only for a legacy (ttl=None) update: pf-client-core (the Deck haptic
  keep-alive is now deadline-bounded so it can't sustain a host-stopped rumble),
  clients/windows (SDL duration), android (JNI packs the lease out-of-band in bit
  48 so any u16 ttl is unambiguous; Kotlin createOneShot(ttl)), apple
  (RumbleRenderer.envelopeDeadline + nextRumble2; sessionStaleSeconds demoted to
  the legacy fallback).
- tests: codec round-trip + tail tolerance + seq-gate reorder (Rust); the probe
  asserts the v2 tail arrived under PUNKTFUNK_TEST_FEEDBACK; the Apple loopback
  asserts ttlMs round-trips end to end; RumbleTuning lease-decision cases.

The host-side idle-timeout from the previous commit is defense in depth on the
game side; this is the guarantee on the client side. Design:
punktfunk-planning/design/rumble-envelope-plan.md.

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

clients/apple/Sources/PunktfunkKit/Connection/PunktfunkConnection.swift

@@ -570,7 +570,8 @@ public final class PunktfunkConnection {
 
     /// Pull the next force-feedback update for the GCController haptics engine:
     /// `(pad, lowFrequency, highFrequency)` with 0...0xFFFF amplitudes, (0, 0) = stop.
-    /// Drain from the (single) feedback thread, alongside `nextHidOutput`.
+    /// Drain from the (single) feedback thread, alongside `nextHidOutput`. Drops the v2
+    /// self-termination TTL — use `nextRumble2` to honor the host lease.
     public func nextRumble(timeoutMs: UInt32 = 0) throws -> (pad: UInt16, low: UInt16, high: UInt16)? {
         feedbackLock.lock()
         defer { feedbackLock.unlock() }
@@ -590,6 +591,33 @@ public final class PunktfunkConnection {
         }
     }
 
+    /// Pull the next force-feedback update *including its self-termination TTL* (v2 envelopes):
+    /// `(pad, low, high, ttlMs)`. `ttlMs` is how long to render this level before silencing unless
+    /// the host renews it; `RumbleTuning.noTTL` (`UInt32.max`) means "no lease" — a legacy host, so
+    /// fall back to a client-side staleness timeout. The reorder gate (seq) already ran in the
+    /// core, so a stale/reordered envelope never surfaces here. Drain from the (single) feedback
+    /// thread, alongside `nextHidOutput`.
+    public func nextRumble2(timeoutMs: UInt32 = 0) throws
+        -> (pad: UInt16, low: UInt16, high: UInt16, ttlMs: UInt32)?
+    {
+        feedbackLock.lock()
+        defer { feedbackLock.unlock() }
+        guard let h = liveHandle() else { throw PunktfunkClientError.closed }
+
+        var pad: UInt16 = 0, low: UInt16 = 0, high: UInt16 = 0, ttl: UInt32 = .max
+        let rc = punktfunk_connection_next_rumble2(h, &pad, &low, &high, &ttl, timeoutMs)
+        switch rc {
+        case statusOK:
+            return (pad, low, high, ttl)
+        case statusNoFrame:
+            return nil
+        case statusClosed:
+            throw PunktfunkClientError.closed
+        default:
+            throw PunktfunkClientError.status(rc)
+        }
+    }
+
     /// One DualSense feedback event a game wrote to the host's virtual pad — replay it on
     /// the real controller (GCDeviceLight, GCControllerPlayerIndex,
     /// GCDualSenseAdaptiveTrigger). Only a `.dualSense` session emits these.