chore: migrate rust/image-classification to icp-cli

[marc0olo]

Summary

Migrates rust/image-classification from dfx to icp-cli.

• Replaces dfx.json with icp.yaml using custom build steps (WASI compile → wasi2ic → wasm-opt → ic-wasm metadata embed)
• Moves source from src/backend/ and src/frontend/ to flat backend/ and frontend/ layout
• Migrates frontend from webpack + dfx declarations to Vite + @icp-sdk/bindgen
• Adds Makefile with make test exercising the run() query endpoint
• Adds CI workflow image-classification.yml with tool installation steps for wasm32-wasi, wasi2ic, and wasm-opt
• Deletes legacy rust-image-classification-example.yaml, dfx.json, build.sh, webpack.config.js

Test plan

• CI passes
• ./download_model.sh && icp network start -d && icp deploy && make test succeeds locally