[kraenhansen]

Adds ferric build --cwd <path>, as agreed in #195, mirroring napi-rs' --cwd. This supersedes #205 (thanks to dougg0k for the original work), leaving out its dist output change and dependency bumps.

• --cwd resolves against the invocation directory, so relative and absolute paths both work, and it applies to every cargo and napi-rs call, including --clean and --dts-only.
• --output defaults to the --cwd directory. An explicit relative --output still resolves against the invocation directory.
• Cargo is spawned with cwd rather than --manifest-path, so the crate's .cargo/config.toml and toolchain files still apply.
• The target directory comes from cargo metadata, and the library is picked by its exact name, so workspace members and CARGO_TARGET_DIR work and a stale local target/ is ignored.
• The installed-targets and napi feature checks run from the --cwd directory, so a crate's rust-toolchain.toml is respected.
• cargo metadata output is validated with zod.

Test plan

• pnpm run build, pnpm run lint, pnpm run prettier:check
• pnpm --filter ferric-cli run test, with a CLI test that scaffolds a crate via ferric init and builds it with --cwd
• ferric build --cwd packages/ferric-example --target aarch64-apple-ios-sim from the repo root puts the outputs in the crate directory
• --dts-only with a relative --cwd, with an absolute --cwd plus relative --output, and with no --cwd from the crate directory
• A missing --cwd directory gives a clear error
• Two-member workspace, a stale local target/, and CARGO_TARGET_DIR on aarch64-apple-ios-sim
• Toolchain check run from the --cwd directory, using a stand-in rustup
• Android target through --cwd
• --clean through --cwd

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