feat(server): accuracy sprint 001 — Kalman tracker, multi-node fusion, eigenvalue counting

Original work by @taylorjdawson (PR #341). Merged with v0.5.5 firmware
preserved (ADR-069 feature vectors, ADR-073 channel hopping, batch-limited
watchdog from #266 fix).

New server features:
- Kalman tracker bridge for temporal smoothing
- Multi-node CSI fusion with field model
- Eigenvalue-based person counting
- Calibration endpoints (start/stop/status)
- Node positions parsing
- Adaptive classifier enhancements

Co-Authored-By: taylorjdawson <taylor@users.noreply.github.com>
Co-Authored-By: claude-flow <ruv@ruv.net>

data/recordings/pretrain-1775182186.csi.meta.json

@@ -0,0 +1,15 @@
+{
+  "id": "pretrain-1775182186",
+  "name": "pretrain-1775182186",
+  "label": "mixed-activity",
+  "started_at": "2026-04-03T02:09:46Z",
+  "ended_at": "2026-04-03T02:11:46Z",
+  "duration_secs": 120,
+  "frame_count": 5783,
+  "file_size_bytes": 2580539,
+  "file_path": "data/recordings\\pretrain-1775182186.csi.jsonl",
+  "nodes": {
+    "2": 2886,
+    "1": 2897
+  }
+}