Migrate repository from npm to pnpm

[Copilot]

Migrates the monorepo from npm to pnpm as the package manager. pnpm's strict dependency resolution exposed phantom dependencies that were previously masked by npm's flat hoisting.

Package Manager Migration

• Replaced package-lock.json with pnpm-lock.yaml (lockfile v9.0)
• Created pnpm-workspace.yaml for workspace configuration
• Updated lerna.json npmClient to pnpm
• Updated devcontainer to install pnpm on creation

Dependency Resolution Fixes

pnpm's strict isolation revealed missing direct dependencies:

core package:

• globals, type-fest (used in code but not declared)

react package:

• globals, @types/node (required by source files)
• @eslint/js, typescript-eslint, eslint-config-prettier, eslint-plugin-jest, eslint, typescript (required by eslint.config.mjs)

Script Updates

Updated all package.json scripts to use pnpm syntax with proper -- separator:

"test": "pnpm run jest -- --maxWorkers=50%"

Test Infrastructure

• Updated test-project.ts to copy pnpm-lock.yaml instead of package-lock.json
• Fixed PackageManagerService.spec.ts to remove all lock files before testing specific package managers
• Updated snapshots for pnpm command generation in migrations

Known Issue: 2 e2e tests fail due to pre-existing patch-package error when installing Vite dependencies (unrelated to pnpm migration).

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