fix: build per-version Vite stats through the vite-plus toolchain

[Boshen]

Problem

tools/override-vite.mjs (run by the Update Vite Stats workflow via vp run generate) was still written for the old plain-Vite setup and no longer builds anything after the vite-plus migration in #183:

• It pinned the Vite version by writing devDependencies.vite in apps/dashboard/package.json, but the dashboard now depends on vite-plus. The actual vite package is catalog-aliased and resolved through the overrides entry in pnpm-workspace.yaml.
• It built with ./node_modules/vite/bin/vite.js build, which no longer exists — builds now go through vp build.
• It shelled out to pnpm install directly instead of vp install.

Fix

• Pin the target Vite version through the pnpm overrides entry in pnpm-workspace.yaml — the supported way to make vite-plus resolve a specific Vite release.
• Install with vp install and build with vp build (in apps/dashboard).
• Snapshot and restore pnpm-workspace.yaml (plus a final vp install) so the stats run leaves the repo clean.
• Hoist getFilesRecursively to module scope to clear a lint warning.

Verification

Validated the full pipeline locally by overriding to a real vite@7.1.12 (no stable Vite 8 exists yet): vp install resolved real vite@7.1.12 and vp build produced a dist successfully. vp check passes (0 errors).