fix: reject unknown --format values in validate, lint, and doctor

[sjh9714]

Summary

• Fixes Reject unknown --format values instead of silently printing human output #37.
• Validate --format during argument parsing for validate, lint, and
  doctor, so typos fail with the accepted values instead of silently using
  human output.

Test plan

• Added or updated tests where appropriate
• Ran cargo test --locked --workspace
• Reviewed snapshot results; no snapshot changes were produced
• Updated user-facing CLI help to list the accepted format values
• PR title follows Conventional Commits and is under 72 characters

Additional checks:

• cargo test --locked -p weaveffi-cli --bin weaveffi rejects_unknown_human_json_output_formats
• cargo test --locked -p weaveffi-cli
• cargo fmt --all --check
• cargo clippy --locked -p weaveffi-cli --all-targets --no-deps -- -D warnings

Notes for reviewers

extract, format, and schema keep their existing command-specific format
handling. The full workspace Clippy command was also attempted, but Rust 1.95
reports three pre-existing collapsible_match warnings in unchanged
crates/weaveffi-core/src/validate/rules.rs.

[owenthcarey]

Thanks for a great first contribution!