feat(releaser): add --verbose flag for configuration and decision tracing

- Prints a configuration table on startup showing each key, its value,
  and the source (default / config file / env: VARNAME / flag: --name)
- Lists every commit since the last tag with its parsed type and
  the version-bump decision (feat/fix/breaking → patch bump, or ignored)
- Explains the final version choice: highest commit type → next tag
- All verbose output goes to stderr so it never pollutes stdout captures
- Sources tracking wired through config.LoadWithSources and
  ApplyEnvWithSources; LoadWithSources uses a two-pass approach to
  detect which YAML fields were explicitly set vs defaulted

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ROADMAP.md

@@ -66,6 +66,7 @@
 
 - [x] ~~Integration tests against a real Git repo (with fixture commits and tags)~~ — ✓ shipped v0.4.0 (96% coverage, real in-memory repos)
 - [x] ~~Cross-compilation in CI (linux/amd64, linux/arm64, darwin/amd64)~~ — ✓ shipped v0.4.0 (Gitea release workflow, + darwin/arm64 + windows/amd64)
+- [x] ~~`--verbose` flag~~ — ✓ shipped v1.1.1 (shows config sources, commit analysis, version decision)
 - [ ] Documentation site
 
 ## Future / backlog