feat: interactive release confirmation (`--interactive` flag)

[mwaldheim]

Summary

Add a --interactive flag to semrel release that pauses before tagging and asks the user to confirm (or manually override) the detected version bump.

Motivation

Automated commit analysis is reliable for well-maintained commit histories, but there are cases where a human sanity-check is desirable:

• Squash-merged PRs where the merge commit message may not reflect the actual change
• First release of a new major version
• Local developer workflows where the user wants to see the proposed changelog before committing

Proposed UX

$ semrel release --interactive

Analyzing commits since v1.2.3...
  feat: add file storage backend
  fix: correct pagination offset calculation

Proposed next version: v1.3.0 (minor bump)

Changelog preview:
  ### Features
  - add file storage backend

  ### Bug Fixes
  - correct pagination offset calculation

Proceed with v1.3.0? [Y/n/edit]

Options:

• Y — proceed with detected version
• n — abort release
• edit — open $EDITOR with the version number pre-filled for manual override

Acceptance criteria

• --interactive flag available on semrel release
• Shows detected version and changelog preview
• Supports Y/n/edit prompt
• Non-interactive (CI) environments: if stdin is not a TTY and --interactive is set, print an error and exit non-zero
• Compatible with --dry-run (dry-run preview still shown, no actual release)