chore: migrate to devEngines packageManager, pnpm@11

[mizdra]

Summary

• Replace the packageManager field with devEngines.packageManager and bump to pnpm@11
• Move vite/vite-plus to a pnpm catalog entry
• Remove the now-unnecessary blockExoticSubdeps option
• Skip the postinstall scripts for @vscode/vsce-sign and esbuild in allowBuilds, since neither is needed for this repo's actual release flow (vsce publish never uses --sign-tool, and pnpm already installs the correct esbuild platform binary via optionalDependencies)

Test plan

• pnpm install (including a clean reinstall) completes without errors
• pnpm exec esbuild --version and pnpm exec vsce --version both work with the build scripts skipped
• CI passes on this PR

[changeset-bot]

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Latest commit: 532b53f

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