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>

crates/punktfunk-core/src/abi.rs

@@ -1406,7 +1406,7 @@ pub struct PunktfunkProbeResult {
 }
 
 /// Start a bandwidth speed test: ask the host to burst filler over the data plane at
-/// `target_kbps` of goodput for `duration_ms` (each clamped host-side to ≤ 1 Gbps / ≤ 5 s),
+/// `target_kbps` of goodput for `duration_ms` (each clamped host-side to ≤ 3 Gbps / ≤ 5 s),
 /// *briefly pausing video*. Non-blocking — poll [`punktfunk_connection_probe_result`] until its
 /// `done` field is 1. Starting a probe resets any prior measurement.
 ///

crates/punktfunk-core/src/client.rs

@@ -366,7 +366,7 @@ impl NativeClient {
     /// `target_kbps` of goodput for `duration_ms`, *briefly pausing video*. Non-blocking — the
     /// measurement accumulates in the background; poll [`NativeClient::probe_result`] until its
     /// `done` flag is set. Starting a probe resets any prior measurement. The host clamps both
-    /// fields (≤ 1 Gbps, ≤ 5 s).
+    /// fields (≤ 3 Gbps, ≤ 5 s).
     pub fn request_probe(&self, target_kbps: u32, duration_ms: u32) -> Result<()> {
         // Reset the accumulator so a fresh run doesn't blend into the previous one.
         *self.probe.lock().unwrap() = ProbeState {