docs(skills): record the fresh-worktree build:wp and boundary-gate traps

[DavidBabinec]

The run-and-test skill claimed bun install is the only setup a worktree needs. In a fresh worktree two gate steps fail before anything is wrong: the first build:wp exits 1 while vite.config.js creates the missing packages/wp/.env, and check:open-source crashes with ENOENT on packages/figma/dist or packages/wp/dist until both bundles exist. The skill now documents both, and the gate section says check:open-source must follow the two builds.

I left the script alone rather than making it skip a missing dist. A skip would print "passed for all" without reading the bundles, which is the false green the gate exists to prevent.

Verification

Reproduced in a fresh worktree after bun install --frozen-lockfile:

check:open-source   # exit 1, ENOENT scandir packages/figma/dist
build:wp            # exit 1, "Missing: APP_ENV", .env created
build:wp            # exit 0
build:figma         # exit 0
check:open-source   # exit 0, passed for all