Bundled RECTGTN HTN planning domains and problems, embedded into this module at compile time.

taskweft_plans ships priv/plans/{domains,problems}/*.jsonld (plus a handful of *.notes.json siblings). Prior to this module, callers (e.g. taskweft_mcp's resource handlers) read those files off disk at runtime via :code.priv_dir(:taskweft_plans) — fragile under some release/ container packaging setups, where a dependency's priv/ can end up missing from the assembled release even though it's listed in package: files: (the same failure class taskweft/taskweft's Taskweft.JSONLD.Loader documents for its own bundled JSON schema: a path that resolves correctly under mix run but points at a directory that never exists in the runtime image).

Baking file content into the .beam at compile time sidesteps the packaging question entirely — the data travels with the module no matter how the release is assembled, and callers no longer need :code.priv_dir/1 at all. @external_resource on every bundled file makes mix compile recompile this module whenever a plan file changes, so the dev workflow (edit .jsonld, mix test) still works exactly as before.

Every getter returns the exact raw file bytes (not a decoded/re-encoded term) — this module has no JSON dependency, and byte-for-byte content is what MCP resource reads have always served.