fix: re-enable changelogs so release PRs accumulate correctly

With skip-changelog: true, release-please didn't update the PR body
when new commits landed because the tree SHA was unchanged (no
changelog file to diff). Re-enabling changelogs means each new commit
produces different changelog content, forcing release-please to update
both the branch and PR body.

.github/release-please-config.json

@@ -7,7 +7,6 @@
     ".": {
       "release-type": "simple",
       "package-name": "cli",
-      "skip-changelog": true,
       "extra-files": [
         {
           "type": "json",
@@ -19,7 +18,6 @@
     "plugins/compound-engineering": {
       "release-type": "simple",
       "package-name": "compound-engineering",
-      "skip-changelog": true,
       "extra-files": [
         {
           "type": "json",
@@ -36,7 +34,6 @@
     "plugins/coding-tutor": {
       "release-type": "simple",
       "package-name": "coding-tutor",
-      "skip-changelog": true,
       "extra-files": [
         {
           "type": "json",
@@ -53,7 +50,6 @@
     ".claude-plugin": {
       "release-type": "simple",
       "package-name": "marketplace",
-      "skip-changelog": true,
       "extra-files": [
         {
           "type": "json",