chore: remove empty stub crates wifi-densepose-{api,db,config} (closes #578) (#608)

Each of these crates was a single-line doc-comment placeholder:

  v2/crates/wifi-densepose-api/src/lib.rs:    //! WiFi-DensePose REST API (stub)
  v2/crates/wifi-densepose-db/src/lib.rs:     //! WiFi-DensePose database layer (stub)
  v2/crates/wifi-densepose-config/src/lib.rs: //! WiFi-DensePose configuration (stub)

with empty [dependencies] in their Cargo.toml and zero references from any
source file or Cargo.toml in the workspace (verified by `grep -rln
wifi-densepose-api/-db/-config` across `v2/`). They were reserved early for
an envisioned REST/database/config split that never materialised.

The functionality these would have provided is covered today by:
- REST/WS:  wifi-densepose-sensing-server (Axum)
- Config:   per-crate config + CLI args in sensing-server and desktop
- DB:       no persistent state; system is real-time

Removal prevents `cargo` from listing dead crates, shipping empty published
artifacts to crates.io, or wasting reviewer attention. If any of these names
is needed in the future, reintroduce them with a real implementation.

Per the issue reporter (@bannned-bit / Matad0r) #578 explicitly listed
"OR be removed from workspace members until implementation starts" as an
acceptable resolution.

Updated:
- `v2/Cargo.toml`: drop the three members (with inline comment explaining why)
- `v2/Cargo.lock`: regenerated by cargo check
- `CLAUDE.md`: drop the three rows from the crate table and the publishing
  order list
- `CHANGELOG.md`: add an `[Unreleased] / Removed` entry

Verified:
- `cd v2 && cargo check --workspace --no-default-features` -> finished
  in 48s, no errors (warnings unchanged)

CLAUDE.md

@@ -14,9 +14,6 @@ Dual codebase: Python v1 (`v1/`) and Rust port (`v2/`).
 | `wifi-densepose-mat` | Mass Casualty Assessment Tool — disaster survivor detection |
 | `wifi-densepose-hardware` | ESP32 aggregator, TDM protocol, channel hopping firmware |
 | `wifi-densepose-ruvector` | RuVector v2.0.4 integration + cross-viewpoint fusion (5 modules) |
-| `wifi-densepose-api` | REST API (Axum) |
-| `wifi-densepose-db` | Database layer (Postgres, SQLite, Redis) |
-| `wifi-densepose-config` | Configuration management |
 | `wifi-densepose-wasm` | WebAssembly bindings for browser deployment |
 | `wifi-densepose-cli` | CLI tool (`wifi-densepose` binary) |
 | `wifi-densepose-sensing-server` | Lightweight Axum server for WiFi sensing UI |
@@ -135,17 +132,14 @@ Crates must be published in dependency order:
 2. `wifi-densepose-vitals` (no internal deps)
 3. `wifi-densepose-wifiscan` (no internal deps)
 4. `wifi-densepose-hardware` (no internal deps)
-5. `wifi-densepose-config` (no internal deps)
-6. `wifi-densepose-db` (no internal deps)
-7. `wifi-densepose-signal` (depends on core)
-8. `wifi-densepose-nn` (no internal deps, workspace only)
-9. `wifi-densepose-ruvector` (no internal deps, workspace only)
-10. `wifi-densepose-train` (depends on signal, nn)
-11. `wifi-densepose-mat` (depends on core, signal, nn)
-12. `wifi-densepose-api` (no internal deps)
-13. `wifi-densepose-wasm` (depends on mat)
-14. `wifi-densepose-sensing-server` (depends on wifiscan)
-15. `wifi-densepose-cli` (depends on mat)
+5. `wifi-densepose-signal` (depends on core)
+6. `wifi-densepose-nn` (no internal deps, workspace only)
+7. `wifi-densepose-ruvector` (no internal deps, workspace only)
+8. `wifi-densepose-train` (depends on signal, nn)
+9. `wifi-densepose-mat` (depends on core, signal, nn)
+10. `wifi-densepose-wasm` (depends on mat)
+11. `wifi-densepose-sensing-server` (depends on wifiscan)
+12. `wifi-densepose-cli` (depends on mat)
 
 ### Validation & Witness Verification (ADR-028)