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/notes/notes.go

@@ -2,38 +2,16 @@ package notes
 
 import (
 	"fmt"
-	"regexp"
 	"strings"
 
 	"git.k3nny.fr/releaser/internal/commits"
 )
 
-// headerSubjectRe captures the subject (description) part of a conventional commit header.
-var headerSubjectRe = regexp.MustCompile(`(?i)^\w+(?:\([^)]*\))?!?\s*:\s*(.+)`)
-
 // Generate produces grouped markdown release notes from a list of commit messages.
 // Commits are grouped into Breaking Changes, Features, and Bug Fixes.
 // Commits with no releasable type are omitted.
 func Generate(tagName string, messages []string) string {
-	var breaking, feats, fixes []string
-
-	for _, msg := range messages {
-		t := commits.Parse(msg)
-		if t == commits.TypeNone {
-			continue
-		}
-		first := strings.SplitN(strings.TrimSpace(msg), "\n", 2)[0]
-		subject := extractSubject(first)
-
-		switch t {
-		case commits.TypeBreaking:
-			breaking = append(breaking, subject)
-		case commits.TypeFeat:
-			feats = append(feats, subject)
-		case commits.TypeFix:
-			fixes = append(fixes, subject)
-		}
-	}
+	breaking, feats, fixes := commits.Group(messages)
 
 	var sb strings.Builder
 	fmt.Fprintf(&sb, "## %s\n", tagName)
@@ -53,13 +31,3 @@ func writeSection(sb *strings.Builder, title string, items []string) {
 		fmt.Fprintf(sb, "- %s\n", item)
 	}
 }
-
-// extractSubject returns the description part of a conventional commit header.
-// Falls back to the 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)
-}