feat(bfld): runnable e2e BFI decode tool (ADR-365)

Adds `examples/bfi_decode.rs`: read a radiotap pcap, decode every VHT
beamforming report, print the report-rate dashboard (decoded/sec, gaps,
dupes, failures) and the motion-energy series. Ties capture -> cbr ->
features into one runnable front-end.

  cargo run -p wifi-densepose-bfld --example bfi_decode -- capture.pcap

Verified on a 3-report synthetic pcap (decoded 3, 1 seq gap, 6.67/s).
Values are only as real as the capture; a real capture is still hardware-
gated (see ADR-365). clippy -D warnings clean.

Co-Authored-By: claude-flow <ruv@ruv.net>

v2/crates/wifi-densepose-bfld/examples/bfi_decode.rs

@@ -0,0 +1,77 @@
+//! End-to-end BFI decode tool: read a radiotap pcap, decode every VHT
+//! Compressed Beamforming Report, and print a report-rate dashboard plus the
+//! motion-energy time series (ADR-365).
+//!
+//! This is the runnable front-end for the BFLD BFI path. It works on any
+//! `LINKTYPE_IEEE802_11_RADIOTAP` pcap; the values it prints are only as real
+//! as the capture — a synthetic pcap yields synthetic numbers.
+//!
+//! Run with:
+//! ```sh
+//! cargo run -p wifi-densepose-bfld --example bfi_decode -- capture.pcap
+//! ```
+
+use std::process::ExitCode;
+
+use wifi_densepose_bfld::capture::decode_pcap;
+use wifi_densepose_bfld::features::motion_series;
+
+fn main() -> ExitCode {
+    let Some(path) = std::env::args().nth(1) else {
+        eprintln!("usage: bfi_decode <capture.pcap>");
+        return ExitCode::from(2);
+    };
+    let bytes = match std::fs::read(&path) {
+        Ok(b) => b,
+        Err(e) => {
+            eprintln!("cannot read {path}: {e}");
+            return ExitCode::from(2);
+        }
+    };
+    let (reports, summary) = match decode_pcap(&bytes) {
+        Ok(v) => v,
+        Err(e) => {
+            eprintln!("not a usable capture: {e}");
+            return ExitCode::from(1);
+        }
+    };
+
+    println!("== BFI report-rate dashboard ({path}) ==");
+    println!("frames examined:     {}", summary.frames);
+    println!("action frames:       {}", summary.action_frames);
+    println!("beamforming decoded: {}", summary.decoded);
+    println!("decode failures:     {}", summary.decode_failures);
+    println!("sequence gaps:       {}", summary.sequence_gaps);
+    println!("sequence dupes:      {}", summary.sequence_dupes);
+    println!("reports/sec:         {:.2}", summary.reports_per_sec());
+
+    if let Some(first) = reports.first() {
+        let c = &first.report.control;
+        println!(
+            "first report:        Nr{}xNc{} {}MHz Ng{:?} {} avg_snr={:?}",
+            c.nr,
+            c.nc,
+            c.width.mhz(),
+            c.grouping,
+            if c.mu { "MU" } else { "SU" },
+            first.report.avg_snr,
+        );
+    }
+
+    let series = motion_series(&reports);
+    if series.is_empty() {
+        println!("motion series:       (need >=2 same-dimension reports)");
+    } else {
+        let peak = series.iter().map(|&(_, e)| e).fold(0.0_f64, f64::max);
+        let mean = series.iter().map(|&(_, e)| e).sum::<f64>() / series.len() as f64;
+        println!("motion samples:      {} (mean {mean:.4}, peak {peak:.4})", series.len());
+    }
+
+    if summary.decoded == 0 {
+        eprintln!(
+            "note: zero beamforming reports. On 2.4 GHz there are none (VHT/HE is 5/6 GHz); \
+             confirm the client is on a 5 GHz SSID and the monitor is on its exact channel+width."
+        );
+    }
+    ExitCode::SUCCESS
+}