refactor: split into monorepo with core library and action packages (#19)

* refactor: split into monorepo with core library and action packages

Extract Slack message composition and posting logic into a standalone
`@sixt/slack-message` core package with zero dependencies (native fetch
only). The GitHub Action is refactored to depend on the core package for
block composition and message posting, removing the `@slack/web-api`
dependency entirely.

- packages/core: @sixt/slack-message with compose(), postMessage(), and
  block builder functions
- packages/action: GitHub Action using @actions/core + core package
- Upgrade Jest 26 -> 29, @vercel/ncc 0.26 -> 0.38 for Node 18+
  compatibility
- All 43 existing tests preserved and passing

* chore: update all dependencies to latest versions

- TypeScript 4.1 → 5.9
- ESLint 7 → 9 (migrate .eslintrc.js to flat config eslint.config.js)
- @typescript-eslint 4 → 8
- Jest 29.7 (latest 29.x, ts-jest doesn't support 30 yet)
- Prettier 2 → 3
- nock 13 → 14
- @actions/core 1.9 → 1.11 (latest CJS-compatible)
- @actions/github 4 → 6 (latest CJS-compatible, .rest.* API)
- @vercel/ncc 0.38 (already updated)
- Drop @slack/web-api, eslint-config-prettier/typescript, jest-circus
- 0 npm audit vulnerabilities (down from 31)
- Bundle size 894KB → 602KB

* ci: add e2e test workflow for manual validation

workflow_dispatch workflow that posts test messages to a Slack channel,
covering: basic messages, field enrichment, buttons + changelog,
mention injection, and custom blocks.

* fix: branch field not clickable on pull request events

The ref check used `ref.includes('pulls')` but PR refs are
`refs/pull/N/merge` (singular), so the condition never matched.
Changed to `ref.includes('pull/')`.

* feat: add field() and link() helpers to core package

Convenience functions so core package callers can produce the same
rich mrkdwn formatting (bold labels, 2-column grid, clickable links)
as the GitHub Action without manual string construction.

* chore: commit core package dist for git dependency consumers

Remove packages/core/dist from .gitignore so that consumers installing
@sixt/slack-message as a git dependency get the pre-built output.

* feat: add core tests, return ts from postMessage, fix orphaned divider

- Add 46 unit tests for core package covering block builders,
  compose(), mention/injectMention, iconForStatus, and postMessage
- postMessage now returns { ts, channel } for threading/updating
- Divider is only added when footerText is provided (no orphan)
- Export PostMessageResult type

* chore: remove e2e test workflow

* chore: drop source maps from core dist

* fix: validate postMessage response, remove redundant re-export

- Replace non-null assertions with explicit validation in postMessage
- Remove redundant iconForStatus re-export from action client
- Update test helper to import iconForStatus from core package

* feat: add /core subpath export for clean consumer imports

* ci: add github packages publishing for @sixt/slack-message

- Add publishConfig, files, repository, prepublishOnly to core package
- Add workflow_dispatch publish workflow (manual trigger with version input)
- Published package is 3.4KB — just dist/ with zero dependencies

Consumers add to .npmrc:
  @Sixt:registry=https://npm.pkg.github.com

Then install normally:
  npm install @sixt/slack-message

* fix: simplify publish workflow, remove git push step

Author: kaanbiryol

.eslintignore

@@ -0,0 +1,27 @@
+name: Publish @sixt/slack-message
+on:
+  workflow_dispatch:
+    inputs:
+      version:
+        description: 'Version to publish (e.g. 0.2.0)'
+        required: true
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    permissions:
+      packages: write
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          registry-url: https://npm.pkg.github.com
+
+      - run: npm ci
+      - run: npm test -w @sixt/slack-message
+      - run: npm version ${{ inputs.version }} --no-git-tag-version -w packages/core
+      - run: npm publish -w packages/core
+        env:
+          NODE_AUTH_TOKEN: ${{ secrets.GITHUB_TOKEN }}

.eslintrc.js

@@ -117,5 +117,6 @@ out
 .yarn/install-state.gz
 .pnp.*
 
-# ncc
-lib
+# Build output
+lib
+packages/action/lib

.github/workflows/publish-core.yml

@@ -72,4 +72,4 @@ inputs:
     required: false
 runs:
   using: 'node20'
-  main: 'dist/index.js'
+  main: 'packages/action/dist/index.js'

.gitignore

@@ -0,0 +1,30 @@
+const tseslint = require('typescript-eslint');
+const prettier = require('eslint-plugin-prettier');
+const jest = require('eslint-plugin-jest');
+
+module.exports = tseslint.config(
+  {
+    ignores: ['**/coverage/**', '**/dist/**', '**/lib/**', '**/node_modules/**'],
+  },
+  ...tseslint.configs.recommended,
+  {
+    files: ['**/*.ts'],
+    plugins: {
+      prettier,
+    },
+    rules: {
+      'prettier/prettier': 'error',
+    },
+  },
+  {
+    files: ['**/__tests__/**/*.ts'],
+    plugins: {
+      jest,
+    },
+    ...jest.configs['flat/recommended'],
+    rules: {
+      ...jest.configs['flat/recommended'].rules,
+      '@typescript-eslint/no-require-imports': 'off',
+    },
+  },
+);

action.yml

@@ -1,15 +1,3 @@
 module.exports = {
-  clearMocks: true,
-  moduleFileExtensions: ['js', 'ts'],
-  testEnvironment: 'node',
-  testMatch: ['**/*.test.ts'],
-  testRunner: 'jest-circus/runner',
-  transform: {
-    '^.+\\.ts$': 'ts-jest',
-  },
-  verbose: true,
-  coverageDirectory: './coverage/',
-  collectCoverage: true,
-  preset: 'ts-jest',
-  globalSetup: './__tests__/setupTest.ts',
+  projects: ['<rootDir>/packages/core', '<rootDir>/packages/action'],
 };