chore: bump to v0.2.1

[ergofobe]

Summary

• Bump imogen-cli version to 0.2.1 (patch release)
• Unreleased since v0.2.0: submodule pin of imogen-sdk (SDK path dependency is an unpinned sibling checkout, so no commit or release records which SDK it was built against #7, build(sdk): pin imogen-sdk as a git submodule (#7) #8) and move to imogen-sdk v0.3.0 (Move to imogen-sdk 0.3.0 #10, build(sdk): move to imogen-sdk 0.3.0 (#10) #11) — build/infra changes only, no user-visible feature

Test plan

• cargo test --locked — 103 passed, 2 ignored
• cargo fmt --check
• cargo clippy --all-targets --locked -- -D warnings
• cargo build --release --locked
• ./target/release/imogen --version prints imogen 0.2.1

🤖 Generated with Claude Code