feat(client/speedtest): request the host's full 3 Gbps probe ceiling

The Apple speed test asked for only 400 Mbps, capping the measured throughput
there and hiding the link's real headroom. Request the host's full
MAX_PROBE_KBPS (3 Gbps) instead, and raise the recommended-bitrate clamp from
500 Mbps to the host's 2 Gbps session ceiling so a fast measurement yields a
usable recommendation.

Also fix the stale caps left when the host clamps were raised (b8a33e2): the
resolved-bitrate range and the probe doc comments (abi.rs, client.rs,
regenerated header), plus the section 9 roadmap copy, now read 3 Gbps probe /
2 Gbps session.

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

clients/apple/Sources/PunktfunkClient/SessionModel.swift

@@ -77,6 +77,7 @@ final class SessionModel: ObservableObject {
     func connect(to host: StoredHost, width: UInt32, height: UInt32, hz: UInt32,
                  compositor: PunktfunkConnection.Compositor = .auto,
                  gamepad: PunktfunkConnection.GamepadType = .auto,
+                 bitrateKbps: UInt32 = 0,
                  autoTrust: Bool = false) {
         guard phase == .idle else { return }
         phase = .connecting
@@ -93,7 +94,7 @@ final class SessionModel: ObservableObject {
                 host: host.address, port: host.port,
                 width: width, height: height, refreshHz: hz,
                 pinSHA256: pin, identity: identity, compositor: compositor,
-                gamepad: gamepad) }
+                gamepad: gamepad, bitrateKbps: bitrateKbps) }
             await MainActor.run { [weak self] in
                 guard let self else { return }
                 // The user may have abandoned this attempt (window closed, another host