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>

README.md

@@ -1,6 +1,6 @@
 # releaser
 
-![release](https://img.shields.io/badge/release-v1.3.0-blue.svg)
+![release](https://img.shields.io/badge/release-v1.4.0-blue.svg)
 
 A CI-friendly release automation tool for GitFlow workflows using Conventional Commits.
 
@@ -8,22 +8,22 @@ A CI-friendly release automation tool for GitFlow workflows using Conventional C
 
 Standard tools like `semantic-release` are designed for trunk-based development. In a GitFlow setup with versioned release branches (`release/1.1`, `release/1.2`), they either fail to respect the branch's version range or require brittle configuration.
 
-`releaser` is built for this exact workflow: it reads the branch name to pin the `major.minor`, parses Conventional Commits to determine the patch increment, and handles everything from `pom.xml` update to GitLab tag+release creation.
+`releaser` is built for this exact workflow: it reads the branch name to pin the `major.minor`, parses Conventional Commits to determine the patch increment, and handles everything from `pom.xml` update to GitLab/GitHub tag+release creation.
 
 ## How it works
 
 ```
 release/1.2 branch
-  └─ last tag: v1.2.3 (or none → start at v1.2.0)
+  └─ last tag: 1.2.3 (or none → start at 1.2.0)
        └─ commits since tag → Conventional Commits analysis
-            └─ next version: v1.2.4
+            └─ next version: 1.2.4
 ```
 
 1. **Branch parsing** — extracts `major.minor` from branch name (e.g. `release/1.2` → `1.2`)
 2. **Tag discovery** — finds the latest tag matching `major.minor.*` on the current branch
 3. **Commit analysis** — parses Conventional Commits between last tag and HEAD
 4. **Version bump** — increments patch (the minor is owned by the branch)
-5. **Release** — updates `pom.xml`, commits, tags, creates GitLab release
+5. **Release** — updates `pom.xml`, commits, tags, creates GitLab or GitHub release
 
 ## Version bump rules
 
@@ -44,13 +44,13 @@ releaser --init
 # Simulate next version (no side effects)
 releaser --dry-run
 
-# Full release: update pom.xml + CHANGELOG.md, commit, tag, push, GitLab release
+# Full release: update pom.xml + CHANGELOG.md, commit, tag, push, create release
 releaser
 
-# Commit and tag locally — skip push and GitLab release
+# Commit and tag locally — skip push and release creation
 releaser --no-push
 
-# Push commit and tag but skip creating the GitLab release
+# Push commit and tag but skip creating the release
 releaser --no-release
 
 # Update files but stop before committing (review first)
@@ -75,6 +75,9 @@ releaser --tag-prefix ""
 
 # Override branch pattern (e.g. also match hotfix/ branches)
 releaser --branch-pattern "^(?:.*/)?(?:release|hotfix)/(\d+)\.(\d+)$"
+
+# Write dotenv artifact to a custom path (or "" to disable)
+releaser --release-env-file deploy/version.env
 ```
 
 ## Configuration
@@ -88,6 +91,10 @@ git:
   commit_message: "chore(release): {version} [skip ci]"
   author_name: ""                                    # defaults to git config user.name
   author_email: ""                                   # defaults to git config user.email
+  releasable_types:                                  # default: all three
+    - fix
+    - feat
+    - breaking
 
 maven:
   pom_path: "pom.xml"                                # relative to repo root
@@ -96,18 +103,23 @@ gitlab:
   url: "https://gitlab.example.com"                  # or env CI_SERVER_URL
   token: ""                                          # env GITLAB_TOKEN (never commit this)
   project: ""                                        # env CI_PROJECT_ID or CI_PROJECT_PATH
+
+github:
+  token: ""                                          # env GITHUB_TOKEN (never commit this)
+  repo: ""                                           # "owner/repo" format
 ```
 
 ### Environment variables
 
-GitLab-related fields are automatically read from the CI environment if not set in the config file:
+| Variable           | Used for                          |
+|--------------------|-----------------------------------|
+| `GITLAB_TOKEN`     | GitLab API auth + HTTPS push auth |
+| `CI_SERVER_URL`    | GitLab instance URL               |
+| `CI_PROJECT_ID`    | GitLab project identifier (numeric) |
+| `CI_PROJECT_PATH`  | GitLab project identifier (fallback) |
+| `GITHUB_TOKEN`     | GitHub API auth                   |
 
-| Variable          | Used for                          |
-|-------------------|-----------------------------------|
-| `GITLAB_TOKEN`    | API auth + HTTPS push auth        |
-| `CI_SERVER_URL`   | GitLab instance URL               |
-| `CI_PROJECT_ID`   | Project identifier (numeric)      |
-| `CI_PROJECT_PATH` | Project identifier (fallback)     |
+When both `github.*` and `gitlab.*` are configured, GitHub takes precedence.
 
 ## CI integration (GitLab CI example)
 
@@ -121,4 +133,7 @@ release:
     GITLAB_TOKEN: $RELEASE_TOKEN   # project/group CI variable with api + write_repository scope
   script:
     - releaser
+  artifacts:
+    reports:
+      dotenv: release.env          # exposes NEXT_VERSION to downstream jobs
 ```