unityz 0.1.3

CLI contract release. Every command now shares one exit-code and output
contract, so scripts can branch on the status without parsing text.

Added

• trees command: exports the type trees embedded in a bundle, WebFile, or
  serialized file as a --trees JSON table, MonoBehaviour trees keyed by
  their script via the container's MonoScripts (#146).
• diff --trees decodes typeless Mono objects for --fields (#143).
• Directory --json batches wrap each file's output as
  {"file":...,"results":[...]}, with "error" on a failing member (#140).
• show accepts --json as a no-op, so scripts can pass the flag uniformly
  (#142).
• Tag-driven release workflow, this changelog, and prebuilt Linux x86_64 and
  macOS arm64 binaries on each GitHub Release.

Changed

• Usage errors (unknown flag, missing argument, malformed id) exit 2; read,
  decode, and check failures exit 1; the diagnostic always goes to stderr and
  a failing run writes nothing to stdout (#139, #141, #148, #151).
• A file that is not a Unity asset is an error for every command instead of
  a per-command empty success (#140).
• extract on a bundle or WebFile extracts the assets inside its nodes by
  default; --recursive is accepted as a no-op (#148).
• Batch extract and fsb write each input under <outdir>/<file name>/
  so bundles sharing node names cannot overwrite each other (#141, #145).
• edit --out and trees --out are rejected over a directory instead of
  overwriting one output file (#147).
• Every CLI flag is documented in README.md and docs/features.md (#149).

Fixed

• Directory diff stopped after the first matched file and ignored
  --fields (#139).
• verify --path-id N on a missing object reported success (#142).
• edit --patch silently dropped entries naming missing objects on bundles
  and WebFiles; the patch now fails before writing (#150).
• unityz --version reported 0.1.1 while the package declared 0.1.2; the
  version is now derived from build.zig.zon (#144).
• managed exited 0 with no assemblies found or an unparseable assembly
  (#151).