chore: fix gitignore — untrack lock files, commit devtools extension build

- Expand **/pubspec.lock so all sub-package lock files are ignored
  (per dart.dev/guides/libraries/private-files#pubspeclock)
- Add exception for extension/devtools/build/ so the pre-built web
  extension is committed and available without a local rebuild step
- Ignore flutter create boilerplate in devtools_ui (README, test)
- Remove all tracked pubspec.lock files from VCS

Author: Nguyễn Tuấn Việt

.gitignore

@@ -37,15 +37,18 @@ migrate_working_dir/
 #.vscode/
 
 # Flutter/Dart/Pub related
-# Libraries should not include pubspec.lock, per https://dart.dev/guides/libraries/private-files#pubspeclock.
-/pubspec.lock
+# Libraries should not commit pubspec.lock, per https://dart.dev/guides/libraries/private-files#pubspeclock.
+**/pubspec.lock
 **/doc/api/
-.dart_tool/
-.flutter-plugins
-.flutter-plugins-dependencies
-.metadata
+**/.dart_tool/
+**/.flutter-plugins
+**/.flutter-plugins-dependencies
+**/.metadata
 /build/
 **/build/
+# Exception: DevTools extension web build must be committed so pub.dev can serve it.
+!packages/hyper_render_devtools/extension/devtools/build/
+!packages/hyper_render_devtools/extension/devtools/build/**
 /coverage/
 
 # Publish preparation (temporary file generated by scripts/publish.sh)