Migrate package management from npm to pnpm.

Standardize local and CI workflows on pnpm 11.0.8, replace npm commands in docs/config, and swap lockfiles for reproducible installs.

Co-authored-by: Cursor <cursoragent@cursor.com>

.gitignore

@@ -1,7 +1,7 @@
 # Logs
 logs
 *.log
-npm-debug.log*
+pnpm-debug.log*
 yarn-debug.log*
 yarn-error.log*
 lerna-debug.log*
@@ -48,8 +48,8 @@ web_modules/
 # TypeScript cache
 *.tsbuildinfo
 
-# Optional npm cache directory
-.npm
+# Optional pnpm cache directory
+.pnpm-store
 
 # Optional eslint cache
 .eslintcache
@@ -66,7 +66,7 @@ web_modules/
 # Optional REPL history
 .node_repl_history
 
-# Output of 'npm pack'
+# Output of 'pnpm pack'
 *.tgz
 
 # Yarn Integrity file