chore(repo): rename rust-port/wifi-densepose-rs → v2/ (flatten to one level) (#427)

The Rust port lived two directories deep (rust-port/wifi-densepose-rs/)
without any sibling under rust-port/ that warranted the extra level.
Move the whole workspace up to v2/ to match v1/ (Python) at the same
depth and shorten every cd / build command across the repo.

git mv preserves history for all tracked files. 60 files updated for
path references (CI workflows, ADRs, docs, scripts, READMEs, internal
.claude-flow state). Two manual fixes for relative-cd paths in
CLAUDE.md and ADR-043 that became wrong after the depth change
(cd ../.. → cd ..).

Validated:
- cargo check --workspace --no-default-features → clean (after target/
  nuke; the gitignored target/ was carried by the OS rename and had
  hard-coded old paths in build scripts)
- cargo test --workspace --no-default-features → 1,539 passed, 0 failed,
  8 ignored (same totals as pre-rename)
- ESP32-S3 on COM7 → still streaming live CSI (cb #40300, RSSI -64 dBm)

After-merge follow-up: contributors should `rm -rf v2/target` once and
let cargo regenerate from the new path.

scripts/gcloud-train.sh

@@ -263,7 +263,7 @@ export LIBTORCH=\$(python3 -c "import torch; print(torch.__path__[0] + '/lib')")
 export LD_LIBRARY_PATH="\${LIBTORCH}:\${LD_LIBRARY_PATH:-}"
 
 # Build the training binary with tch-backend
-cd ~/wifi-densepose/rust-port/wifi-densepose-rs
+cd ~/wifi-densepose/v2
 echo "Building with LIBTORCH=\$LIBTORCH ..."
 cargo build --release --features tch-backend --bin train 2>&1 | tail -5
 
@@ -325,7 +325,7 @@ set -euo pipefail
 source \$HOME/.cargo/env
 export LIBTORCH=\$(python3 -c \"import torch; print(torch.__path__[0] + '/lib')\")
 export LD_LIBRARY_PATH=\"\${LIBTORCH}:\${LD_LIBRARY_PATH:-}\"
-cd ~/wifi-densepose/rust-port/wifi-densepose-rs
+cd ~/wifi-densepose/v2
 
 # Set auto-shutdown timer (safety net)
 sudo shutdown -P +$((MAX_HOURS * 60)) &
@@ -408,7 +408,7 @@ mkdir -p "$LOCAL_RESULTS"
 
 # Package results on the VM
 gcloud compute ssh "$INSTANCE_NAME" --zone="$ZONE" --command="
-cd ~/wifi-densepose/rust-port/wifi-densepose-rs
+cd ~/wifi-densepose/v2
 tar czf ~/training-artifacts.tar.gz \
     checkpoints/ \
     logs/ \