feat: add pr edit command

[hex2dec]

Summary

• add gitee pr edit for title, body, state, and draft readiness updates
• reuse existing auth, repo inference, canonical repo fallback, and pr view output contracts
• add integration coverage for success paths, validation errors, not found cases, and help discovery

Validation

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

Sample usage

gitee pr edit 42 --repo octo/demo --title "Updated title" --json
printf 'Generated from stdin\n' | gitee pr edit 44 --body-file - --ready

Closes #50