docs: reconcile harness build command schema - #813

…eatures

Audit of docs/reference/ against the code:

- cli.md: Linux installs ship min/mip/minimald only; minvmd is a
  source build (prebuilt amd64 attached to GitHub Releases, no arm64)
  — per scripts/stage-release.sh COMPONENTS and release-pipeline.md.
- minimal-dot-toml.md: rename stale `minimal update`/`minimal
  materialize` to the mip CLI, and cross-reference that `mip update`
  rewrites the upstream and sideload locked_commit fields in place
  (crates/op/src/project/update.rs).
- tasks.md: mip run in the args example; document `description`
  (shown by mip status), the /bin/<cmd> exec resolution, arg defaults
  making arguments optional, and the full arg datatype forms (arrays,
  enums, table form with help/default) per the args crate.
- build-specs.md: replace the line-anchored stdlib blob link with a
  stable file link; tests run by `mip check`.
- harness-specs.md: `mip build` / `mip init` binary names (light
  re-audit after #813).
- sandbox-operations.md: match the in-sandbox helper
  (crates/mctx/src/min_helper.sh + env.rs): --session flag and
  no-flag default, stack.* not harness.* targets, check takes
  --stacks (not --harnesses) and has no --skip-checkers/short flags,
  add the build/test shorthands and patched-pkg, mark the surface
  Linux-only, and add a note disambiguating the helper from the min
  session CLI.
- cli-min.md, cli-mip.md: regenerate the snippets touched by the help
  text fixes (cache clean, login example) from the rebuilt binaries
  at d9f2016.
- crates/minvmd/README.md: replace the stale "persistent data disk is
  a follow-up" note with the shipped per-VM /dev/vdb ext4 volume
  (crates/minvmd/src/volume.rs, spec 08) and update the libkrun
  guidance for the pinned source build (#694), keeping brew as the
  local-dev fallback.
- frontmatter: every reference page now carries title + description.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>