…rust examples

Same split as basic_ibe (#1443): move the Motoko variant to
motoko/vetkeys/basic_bls_signing and flatten the Rust variant to
rust/vetkeys/basic_bls_signing, each self-contained with its own frontend
copy (previously a shared frontend symlinked into motoko/ and rust/ subdirs).

- Frontend: per-language copy; bindings via the @icp-sdk/bindgen Vite plugin
  from the committed backend/backend.did (replaces scripts/gen_bindings.sh);
  dropped eslint; root workspace package.json so `npm run dev` runs from the
  example root.
- Motoko: idiomatic camelCase interface (signMessage, getMySignatures,
  getMyVerificationKey); moc 1.11.0 + --default-persistent-actors (dropped
  `persistent`); dropped unused sha2 dep; committed backend/backend.did.
- Rust: unchanged (snake_case), relocated to the flattened layout.
- READMEs split per language (linked prerequisites); test.sh added (query
  method called with --query); CI split into motoko + rust jobs on the new
  paths. Baked in the two Copilot fixes from #1443 (error message names
  `backend`; --query for the query method).

CODEOWNERS unchanged: /motoko/vetkeys/ and /rust/vetkeys/ both map to
@dfinity/core-protocol.

Verified: Motoko deploy + test.sh + signature survives an upgrade; Rust
cargo build + deploy + test.sh; both frontends build/typecheck/serve.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

…p Makefile

- Bump the Rust recipe to @dfinity/rust@v3.3.0 and rename the Cargo package to
  `backend`, so the recipe no longer needs a custom `package:` in its
  configuration (matches daily_planner and the other migrated rust examples).
- Drop backend/Makefile; advertise candid regeneration directly in the README
  via `icp build backend && candid-extractor … > backend/backend.did`
  (the Makefile's `rm -rf .icp` clean target was also wrong — only .icp/cache
  should ever be wiped, and that isn't advertised elsewhere anyway).

Verified: rust deploy + test.sh pass; `icp build backend` produces backend.wasm.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

… test.sh

Address Copilot review:
- Use `persistent actor class` explicitly (drop the redundant class-level
  `shared` and the `--default-persistent-actors` mops arg). Empirically the
  flag DID persist this main-canister actor class across upgrades — AGENTS.md's
  caveat is about actor classes spawned as sub-WASMs, not a main canister that
  is an actor class for its init arg — but explicit `persistent` is unambiguous
  and matches AGENTS.md's literal guidance. Verified: state survives an upgrade.
- Drop test.sh (motoko + rust) and run deploy-only CI. The example never had a
  test.sh on master; the deploy itself verifies build + install.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

"ask the canister (IC smart contract) to produce" -> "ask the canister to produce".

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>