chore: migrate rust/face-recognition to icp-cli

[marc0olo]

Summary

• Migrates rust/face-recognition from dfx to icp-cli
• Restructures source: src/backend/ → backend/, src/frontend/ → frontend/
• Adds icp.yaml with bare build steps (wasm32-wasip1 + wasi2ic + wasm-opt, required for the Tract ONNX inference engine)
• Adds Vite + @icp-sdk/bindgen frontend replacing webpack
• Adds CI workflow face-recognition.yml using ghcr.io/dfinity/icp-dev-env-rust:1.0.0
• Deletes old dfx-based workflow rust-face-recognition-example.yaml

Note: The backend uses ic-wasi-polyfill + wasi2ic (required by the Tract ONNX library), so the build uses a bare build: with custom steps targeting wasm32-wasip1 instead of the @dfinity/rust recipe.

Test plan

• CI passes
• icp network start -d && icp deploy && make test succeeds locally
• After uploading models (make upload-models), face detection and recognition work in the browser

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