strop v0.21.0

Containers become real workspaces (0037 DC1b), and directory listings scale.

Added

• Language servers run inside attached containers: :containers → browse →
  open a file, and the server's LSP session rides docker exec stdio —
  no SSH daemon, no tools required inside (distroless-safe), no local-path
  fallback. Attach discovery uses XDG/embedded layers; in-container project
  layers join the trust gate when they're read.
• Git in containers: repository discovery (rev-parse) and context inside
  the container through the same bounded exec boundary; per-commit diffs
  inside containers refuse by name this round.
• Container directory listings stream: retention is direct-children only, so
  a 114 MiB image root lists instantly instead of refusing at the 16 MiB
  archive cap. strop-core gained the supervised streaming primitive
  (stream_with) behind it.

Decided

• Container write policy: read-only. docker cp into a container is not an
  atomic conditional save; :w/:w!/:wq on container documents refuse
  with the policy named, never a local-path fallback.