feat: adopt changesets + fix exports, bump to 0.4.0

- Install @changesets/cli with fixed mode (all @uncaged/* packages sync version)
- Fix package exports: add bun condition, point import to dist/
- Bump all packages to 0.4.0 via changeset version
- Auto-generated CHANGELOG.md for each package
- Ignore workflow-dashboard (private)
- Add npm scripts: changeset, version, release
- publish.sh: support workspace:^ prefix matching

Closes #241, Closes #242

.changeset/config.json

@@ -0,0 +1,17 @@
+{
+  "$schema": "https://unpkg.com/@changesets/config@3.1.4/schema.json",
+  "changelog": "@changesets/cli/changelog",
+  "commit": false,
+  "fixed": [
+    [
+      "@uncaged/*"
+    ]
+  ],
+  "linked": [],
+  "access": "restricted",
+  "baseBranch": "main",
+  "updateInternalDependencies": "patch",
+  "ignore": [
+    "@uncaged/workflow-dashboard"
+  ]
+}