Output Flexibility & Contributor Formatting (v1.6.0)

### Background

Users need more control over where the generated release notes are written and how contributors are identified and displayed. Currently, the output location is fixed and contributor names are raw GitHub logins, which may not match team conventions or real names.

This epic introduces configurable output locations, contributor chapter-line formatting, and a user-alias replacement map so teams can fully tailor the presentation of their release notes.

### Goals

- Support configurable output locations for generated release notes (e.g. wiki, file, PR comment) (#77)
- Enable customisable chapter line formatting for contributor sections (#56)
- Provide a configurable map for replacing GitHub usernames with display names or aliases (#97)
- Ensure all output location modes are documented with examples

### Subtasks

- [ ] #77 Provide support for different locations of release notes
- [ ] #56 Chapter line formatting - contributors
- [ ] #97 Map of user replacements

### Related / References

- Depends on contributor formatting groundwork from Epic 1 (#76 — contributor placeholder)
- #97 (user replacement map) feeds directly into #56 (contributor formatting)