cli: scaffold phase 1 asset release commands

Add metin-release CLI with argparse dispatcher, result envelope and
error hierarchy, and the full Phase 1 release subcommand set:

  release inspect         - scan source root
  release build-manifest  - wraps make-manifest.py
  release sign            - wraps sign-manifest.py, enforces mode 600
  release diff-remote     - HEAD each blob hash against a base URL
  release upload-blobs    - rsync release dir minus manifest
  release promote         - rsync manifest.json + signature
  release verify-public   - GET + Ed25519 verify, optional blob sampling
  release publish         - composite of the above with per-stage timings

Respects --json / --verbose / --quiet. Exit codes follow the plan
(1 validation, 2 remote, 3 integrity, 4 reserved for ERP).

README.md

@@ -1,3 +1,33 @@
 # metin-release-cli
 
-Python CLI for orchestrating Metin2 client releases (Phase 1 of metin-release-cli-plan)
+Python CLI that orchestrates Metin2 client releases — builds manifests, signs
+them, uploads content-addressed blobs, and promotes the new release atomically.
+
+Phase 1 wraps `make-manifest.py` and `sign-manifest.py` from the `m2dev-client`
+repo and adds remote diff, upload, promote, and public verification.
+
+## Install
+
+```
+pip install -e .[dev]
+```
+
+## Usage
+
+```
+metin-release --help
+metin-release release inspect --source /path/to/client
+metin-release release publish --source ... --version 2026.04.14-1 ...
+```
+
+Add `--json` to get a machine-parseable envelope on stdout. Exit codes:
+
+| Code | Meaning                              |
+|------|--------------------------------------|
+| 0    | success                              |
+| 1    | operator / validation error          |
+| 2    | remote or network error              |
+| 3    | signing or integrity error           |
+| 4    | reserved (ERP sync, Phase 2+)        |
+
+See `docs/cli.md` for the full command reference.