[SylvainDruaux]

Both wizards ("Start from Lumos" and "Start from Astro") now ask which package manager installs the new site: npm (default) or pnpm.

Commits:

• Remove the unused project:scaffold channel and electron/project/scaffold.ts. The renderer never called it. The handler count in mainBoundaries.test.ts goes from 134 to 133.
• Share one create flow for both wizards: create the files, install, then make the first commit. The Astro wizard reuses the Lumos runner instead of its own copy, and create-astro now runs with --no-install --no-git. The first commit therefore includes the lockfile, and a new site opens with a clean working tree. A stalled scaffolder is stopped after five minutes instead of leaving the wizard stuck on "Creating…".
• While the wizard runs, dots animate after the log's last line, since installs can print nothing for a long time.
• Add a "Package manager" list to both wizards (npm or pnpm). Stacki checks the chosen manager is installed before creating anything, removes the starter's package-lock.json when pnpm is chosen, and installs with it. The Lumos note says which manager installs the site.

Yarn and Bun are not offered yet because they haven't been tested. Modern Yarn skips node_modules by default (Plug'n'Play), which the preview hasn't been checked against. Adding either one later is one entry in CREATE_PACKAGE_MANAGERS plus a test.

viteModules.test.ts: the contract graph cap goes from 48 to 49, because ipcPayloads.ts now imports shared/properties/packageManager.ts to validate the choice.

Tested: the full gate passes. On macOS, both wizards were tested with npm and pnpm: the only lockfile is the chosen manager's, it's in the first commit, and git status is clean.