fix: the npm package shipped a skill that could not inject a plan

.pi/skills/planning-with-files/ is not an IDE mirror, it is the root of
the npm package `planning-with-files`, so its contents are exactly what
`npm install planning-with-files` delivers. It carried 12 of the 20
canonical scripts and a 262-line SKILL.md against the canonical 488.

Missing were inject-plan.sh, gate-stop.sh, ledger-append, ledger-summary
and phase-status. inject-plan.sh is the injection engine, so the npm
channel shipped a skill with no plan injection, no completion gate and
no ledger, and a SKILL.md documenting none of PWF_PLAN_ROOT, the Stop
gate, plan-doctor or attestation beyond a passing mention.

This predates the #213 rename. The directory has been the package root
since 2026-02-04, when it was a Pi-only package and a reduced surface
was correct; #213 made it the project's canonical npm channel without
revisiting the contents.

The SKILL.md body is now the canonical one. The frontmatter `name` stays
`pi-planning-with-files`, deliberately: Pi registers that id, so
renaming it would break `/skill:pi-planning-with-files` for existing
installs. It also stays free of a `metadata.version` field, since
bump-version.py lists it as lagging and a versioned-but-unbumped file
goes stale silently.

sync-ide-folders.py now delivers the 8 missing scripts here so this
cannot drift again.