8b683f8ccb
gen:bundle previously ran gen:docs and gen:docs:reset around the build. Under prepack that reset ran before bun pm pack assembled the tarball, so the published src/ copy of docs-index.generated.txt was empty and consumers importing via subpath (e.g. @oh-my-pi/pi-coding-agent/internal-urls/docs-index) fell through to the missing repo docs/ tree. Restored gen:docs in prepack so postpack owns the reset (matching the original lifecycle), and made gen:bundle assert the embed is populated and fresh instead of touching it, so a direct gen:bundle outside prepack fails with an actionable message. Fixes #3934