Pure directory move plus path fixups: the Rust port ships as pnpm v12,
so the source tree now lives at pnpm/ (alongside pnpm11/, the frozen
TypeScript line). No identifiers change in this pass — crate names
(pacquet-*), the pacquet bin, PACQUET_VERSION, the @pacquet/* npm
package names v11's runPacquet spawns, the .pacquet virtual-store dir,
the benchmark harness's clone dir, and the pacquet-*.yml workflow
filenames (npm trusted publishing is bound to them) all stay for a
follow-up.
Also removes the root /pnpm/ .gitignore entry (build detritus in the
pre-pnpm11 package location): pnpm/ is real source now and must not be
ignored. Developers with a stale generated pnpm/ dir should delete it
before checking out this change.
