fix: NUL-padded safetensors header + stale HF model card (#1480, #1481)

--convert-model rejected the published model.safetensors because its
JSON header is padded to an 8-byte boundary with trailing NUL bytes,
which a strict serde_json::from_slice parse treats as trailing
characters. Trim the padding before parsing, with a regression test
that reproduces the exact boundary-padded shape of the real HF file.

docs/huggingface/MODEL_CARD.md had drifted from the card actually
published on the Hub: every file in its "Files in this repo" table
(pretrained-encoder.onnx, pretrained-heads.onnx, pretrained.rvf,
room-profiles.json) does not exist in ruvnet/wifi-densepose-pretrained.
Replaced it with the content live on the Hub and added a section
documenting the --convert-model / --model RVF conversion path, which
neither card mentioned.

CHANGELOG.md

@@ -24,6 +24,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **`archive/v1` (the original pure-Python implementation) formally deprecated (ADR-187)** — commits `1fb5397dd`, `b1417fb6e`; refs #509, #1125. Added `archive/v1/DEPRECATED.md` (a loud tombstone) and a `> ⚠️ DEPRECATED` notice atop `archive/v1/README.md`, both pointing at the maintained `v2/` workspace and the `wifi-densepose 2.x` / `ruview` pip wheel (ADR-117). Records the honest fact behind #509: `archive/v1`'s `DensePoseHead` is **architecture-only** — random `kaiming_normal_` init with **zero committed checkpoints** under `archive/v1/` (MEASURED by Glob over `**/*.{pth,onnx,safetensors,pt,ckpt,bin}`). The ADR-028 deterministic proof `archive/v1/data/proof/verify.py` stays live and is explicitly out of scope. The same effort added a **"Model weights: what's real, what's not" three-tier table** to `README.md` + `docs/user-guide.md`, separating real-and-validated checkpoints (presence 82.3% held-out temporal-triplet, MM-Fi pose 82.69% torso-PCK@20, `count_v1`) from the real-but-weak on-device `pose_v1` (PCK@20 = 3.0%, runtime `confidence=0` stub, below the ADR-079 ≥35% target) from the architecture-only `archive/v1` head — and caveated every live single-ESP32 17-keypoint advertisement accordingly. Docs/labeling only; no code or model behavior changed.
 
 ### Fixed
+- **`docs/huggingface/MODEL_CARD.md` had drifted from the model card actually published on the Hub (issue #1481).** Every filename in its "Files in this repo" table (`pretrained-encoder.onnx`, `pretrained-heads.onnx`, `pretrained.rvf`, `room-profiles.json`) pointed at files never uploaded to `ruvnet/wifi-densepose-pretrained` — only `config.json` existed. Replaced the in-repo card with the content actually live on the Hub (`model.safetensors`, `model-q{2,4,8}.bin`, `node-{1,2}.json`, `presence-head.json`, `csi-embed-v2.*`, honest v1→v2 retraction of the single-class "100%" presence claim) and added a "Using with the Rust sensing server (RVF conversion)" section documenting the `--convert-model`/`--convert-out` and `--model` auto-convert paths that neither card previously mentioned.
+- **`--convert-model` failed on the published `model.safetensors`: NUL-padded safetensors header rejected by strict JSON parse (issue #1480, #894 follow-up).** The reference safetensors format pads its JSON header to an 8-byte boundary with trailing NUL bytes; `safetensors_to_rvf` (`wifi-densepose-sensing-server/src/model_format.rs`) fed the full declared-length header slice straight to `serde_json::from_slice`, which rejects the padding as "trailing characters." Since the only published full-precision weight file exercises this padding, `--convert-model` could not convert it at all. Fixed by trimming trailing NUL/whitespace bytes before parsing. Pinned by `safetensors_nul_padded_header_converts` (a header padded to the 8-byte boundary, matching the real HF file, converts and round-trips its weights through `ProgressiveLoader`).
 - **In-server training reconnected — "Start Training" no longer silently no-ops; `/ws/train/progress` streams real progress (ADR-186, issue #1233).** The dashboard's Start Training button POSTed a config, got `success:true`, and nothing happened: `/api/v1/train/start` was a stub that flipped a status string and logged one line, and `/ws/train/progress` 404'd. The full pure-Rust trainer in `training_api.rs` (loads recorded CSI, gradient-descent, exports a `.rvf`) already existed but was **orphaned** — never declared as a module (no `mod training_api;`), so it wasn't compiled at all. Fix (`wifi-densepose-sensing-server`): declared the module, reconciled `AppStateInner` (replaced the `training_status`/`training_config` stub fields with a shared `TrainingState` status handle + cooperative cancel flag + a `training_progress_tx` broadcast), deleted the stub handlers, and merged the real `training_api::routes()` (so `/api/v1/train/{start,stop,status,pretrain,lora}` and `/ws/train/progress` resolve under the existing `/api/v1/*` bearer gate). The training core was decoupled from the ~60-field server state so it is unit-testable. **P5 honesty guarantee:** with `RUVIEW_DISABLE_SERVER_TRAINING` set, start returns a structured `{enabled:false, cli:"wifi-densepose train-room"}` HTTP 409 — never a silent success — and the dashboard disables the Start buttons with a CLI tooltip (enablement is surfaced on `/api/v1/train/status`). Pinned by 8 new tests incl. a **live-socket** test that completes a genuine 101 WebSocket handshake and receives a real progress frame after a POST start, a full POST→poll-status→`.rvf`-exists round-trip, a path-traversal rejection, cancellation, and the disabled-409 path. `cargo test -p wifi-densepose-sensing-server -p wifi-densepose-train --no-default-features` — 0 failed.
 - **FastAPI health/metrics endpoints event-loop starvation.** Calling `psutil.cpu_percent(interval=1)` blocked the single-threaded async event loop for 1.0 second on every health check or metrics collection tick, stalling all incoming requests and WebSocket operations. Fixed by changing `cpu_percent` to use non-blocking `interval=None` and offloading all blocking OS metrics gathering to background thread pools via `asyncio.to_thread`. Verified event loop responsiveness via concurrency regression tests.
 - **EngineBridge now honors `WDP_GUARD_INTERVAL_US`/`WDP_SOFT_GUARD_US`/`WDP_TDM_SLOTS`+`WDP_TDM_SLOT_US`** (#1309, PR #1312, @erichkusuki). The governed trust path previously built its multistatic fuser from a hardcoded `MultistaticConfig::default()` (60 ms guard), so multi-node deployments with WiFi/ESP-NOW time sync (10–150 ms drift) failed every governed cycle regardless of configuration — while the startup log claimed the override took effect. New `StreamingEngine::set_multistatic_config()`; `EngineBridge::new()` takes an `Option<MultistaticConfig>` threaded from the same env-derived config as `AppState.multistatic_fuser`. Hardware-verified on a live 2-node ESP32-S3 setup (90 s window, 0 fusion errors; previously every cycle failed).