feat(releaser): release v1.4.0 — GitHub, SSH agent, configurable bumps

- GitHub release support: internal/ghclient (no SDK, minimal HTTP client);
  GITHUB_TOKEN env var; github.token/github.repo config; GitHub takes
  precedence over GitLab when both are configured; publisher interface
  (releasePublisher) in cmd/main.go makes providers interchangeable
- SSH agent push: gitutil.Push() now tries gitssh.NewSSHAgentAuth for
  git@/ssh:// remotes before falling back to the system git binary
- --release-env-file flag: override dotenv artifact path; pass "" to disable
- git.releasable_types config: filter which commit types trigger a bump
  (defaults to fix, feat, breaking); useful for maintenance branches
- commits.Group(), ExtractSubject(), ReleasableSet() exported helpers:
  notes.go and changelog.go now delegate to these instead of duplicating
- CHANGELOG deduplication guard: changelog.Update() is idempotent — skips
  write if ## [version] section already exists
- Always load config sources: LoadWithSources() called unconditionally;
  removes the dual config path that previously only tracked sources in
  --verbose mode
- .releaser.gitlab-ci.yml: adds artifacts: reports: dotenv: release.env

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

internal/commits/commits.go

@@ -5,6 +5,62 @@ import (
 	"strings"
 )
 
+// headerSubjectRe captures the subject (description) from a conventional commit header.
+var headerSubjectRe = regexp.MustCompile(`(?i)^\w+(?:\([^)]*\))?!?\s*:\s*(.+)`)
+
+// ExtractSubject returns the description part of a conventional commit header.
+// Falls back to the trimmed raw header if the pattern does not match.
+func ExtractSubject(header string) string {
+	m := headerSubjectRe.FindStringSubmatch(header)
+	if m != nil {
+		return strings.TrimSpace(m[1])
+	}
+	return strings.TrimSpace(header)
+}
+
+// Group splits messages into breaking changes, features, and fixes.
+// Only the first line of each message is considered; the subject is extracted.
+// Messages with TypeNone are silently dropped.
+func Group(messages []string) (breaking, feats, fixes []string) {
+	for _, msg := range messages {
+		t := Parse(msg)
+		if t == TypeNone {
+			continue
+		}
+		first := strings.SplitN(strings.TrimSpace(msg), "\n", 2)[0]
+		subject := ExtractSubject(first)
+		switch t {
+		case TypeBreaking:
+			breaking = append(breaking, subject)
+		case TypeFeat:
+			feats = append(feats, subject)
+		case TypeFix:
+			fixes = append(fixes, subject)
+		}
+	}
+	return
+}
+
+// ReleasableSet converts a slice of type-name strings to a set for use in version.Next.
+// An empty or nil slice defaults to all three releasable types (fix, feat, breaking).
+func ReleasableSet(typeNames []string) map[Type]bool {
+	if len(typeNames) == 0 {
+		return map[Type]bool{TypeFix: true, TypeFeat: true, TypeBreaking: true}
+	}
+	m := make(map[Type]bool, len(typeNames))
+	for _, name := range typeNames {
+		switch strings.ToLower(name) {
+		case "fix":
+			m[TypeFix] = true
+		case "feat":
+			m[TypeFeat] = true
+		case "breaking":
+			m[TypeBreaking] = true
+		}
+	}
+	return m
+}
+
 // Type represents the semantic weight of a commit for versioning purposes.
 type Type int