fix(#785): type dump-manifests missing dir errors

[Yeachan-Heo]

Summary

• Type dump-manifests --manifests-dir missing-value failures as missing_flag_value
• Add a dump-manifests usage hint for both separated and --manifests-dir= empty forms
• Record ROADMAP 合影合影，笑死了 #785 and add regression coverage

Validation

• cargo test -p rusty-claude-cli --test output_format_contract -- dump_manifests_missing_dir_has_typed_kind_and_hint_785 --nocapture
• cargo test -p rusty-claude-cli classify_error_kind_returns_correct_discriminants -- --nocapture
• cargo fmt --all -- --check

[1716775457damn]

Properly typing the missing-dir failure as missing_flag_value makes the error surface machine-readable and actionable. The usage hint for both separated and --manifests-dir= empty forms is a nice UX touch. Note: there are merge conflicts to resolve.

[Yeachan-Heo]

Thanks for the narrow fix. This is superseded by current main: parse_dump_manifests_args already emits missing_flag_value: --manifests-dir requires a path for both --manifests-dir with no following value and --manifests-dir= with an empty value, with a dump-manifests usage hint. Verification: cargo test --manifest-path rust/Cargo.toml -p rusty-claude-cli dump_manifests_missing_dir_has_typed_kind_and_hint_786 -- --nocapture passed. Closing this PR as duplicate/superseded rather than merging an older patch.