Normalize body input around --body-file -

[hex2dec]

Summary

• normalize stdin body input around --body-file - for write commands
• remove issue comment --body-stdin
• add integration coverage for flag, file, stdin, and invalid body input combinations
• update README examples for issue comments, PR comments, and PR create

Validation

• cargo fmt -- --check
• cargo test
• cargo clippy --all-targets --all-features -- -D warnings

Examples

printf %s "Posted from stdin" | gitee issue comment I123 --repo octo/demo --body-file - --json
printf %sn "Generated from stdin" | gitee pr comment 42 --repo octo/demo --body-file - --json

Removed behavior

$ gitee issue comment I123 --repo octo/demo --body-stdin
unsupported command

Closes #33