build: ship sl0pstatus, and install every plugin the package carries

Phase 3: `make package` now produces a tarball that provably works on a machine
with no node, npm, bun or rust.

Two bugs the clean-room test found, neither visible until a session actually
started:

  - the default layout builds its status bar out of zjstatus, which we were not
    shipping at all (vendored as sl0pstatus/ in the preceding commits)
  - install.sh installed a hardcoded plugin list, so zjstatus.wasm would not
    have reached the config dir even once staged

Also: layouts/*.kdl still pointed at ~/.config/zellij, missed by the rename pass
because that pass only rewrote config.kdl.

Verified end to end, from the tarball, in a throwaway HOME with node/npm/bun/
cargo shadowed by stubs that fail loudly if invoked:

  sl0ppij --version        -> sl0ppij 0.45.0+sl0p1
  pi --version             -> 0.84.1        (on the bundled bun)
  pir --help               -> ok
  sl0ppij -s realtest      -> session starts under a pty, config "Well defined",
                              fork pane titles render, both wasm plugins load,
                              no errors beyond the first-run permission cache

Artifact: sl0ppi-0.1.0-x86_64-linux.tar.gz, 83M, + .sha256.

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