v6.2.0: deprecate Python deltaglider in favor of deltaglider_proxy (Rust) (#9)

The Rust `deltaglider_proxy` ships proxy + CLI + UI in one binary with a
byte-identical wire format. Maintaining both has been a duplication tax
(metadata-namespace fix v6.1.2 had to land twice). This release is the
final feature release; security/bug fixes stop here.

What this commit does:

- CLI: every invocation prints a deprecation notice to stderr pointing
  at github.com/beshu-tech/deltaglider_proxy with a one-line migration
  alias (`alias dg='deltaglider_proxy s3'`). Banner prints once per
  process; suppress via DG_SUPPRESS_DEPRECATION=1 for CI that hasn't
  migrated yet.
- README: prominent deprecation banner at the top with the migration
  command and the archive-timing notice (~1 week after v6.2.0 ships).
- pyproject.toml: description prefixed with "DEPRECATED" so PyPI search
  results show the warning. Classifier moved Beta -> Inactive.
- CHANGELOG: v6.2.0 entry under "Deprecated" documenting the migration
  path + archive plan, preserving the carried-forward Fixed/Changed/
  Added items from Unreleased.

Repo archive timing: Maintainer will archive ~1 week after v6.2.0 hits
PyPI to give users a window to see the stderr notice on their next
update. PyPI installs continue to work indefinitely.

No behaviour changes to the wire format, the CLI surface, or the
metadata schema. Existing buckets remain readable forever.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

README.md

@@ -1,5 +1,40 @@
 # DeltaGlider
 
+> ## ⚠️ DEPRECATED — use [`deltaglider_proxy`](https://github.com/beshu-tech/deltaglider_proxy)
+>
+> This Python package is **deprecated as of v6.2.0** (this is the last
+> feature release). The canonical implementation is now
+> **[`deltaglider_proxy`](https://github.com/beshu-tech/deltaglider_proxy)** —
+> a single Rust binary that ships the S3-compatible proxy, the CLI, and
+> the web UI. Wire format is byte-identical: data written by this tool
+> is readable by `deltaglider_proxy` and vice versa.
+>
+> **Migration:**
+> ```bash
+> # Install the Rust binary (proxy + CLI + UI, one artifact):
+> brew install beshu-tech/tap/deltaglider_proxy
+> # or download from https://github.com/beshu-tech/deltaglider_proxy/releases
+>
+> # Optional alias for Python-style ergonomics:
+> alias dg='deltaglider_proxy s3'
+>
+> # Every Python subcommand has a 1:1 Rust equivalent:
+> deltaglider cp …           →   deltaglider_proxy s3 cp …
+> deltaglider migrate …      →   deltaglider_proxy s3 migrate …
+> deltaglider stats …        →   deltaglider_proxy s3 stats …
+> ```
+>
+> The Python repository will be **archived** approximately one week
+> after the v6.2.0 release. PyPI installs will continue to work
+> indefinitely (PyPI never deletes published versions), but no further
+> updates or security fixes will land here. Open issues and PRs should
+> go to [`deltaglider_proxy`](https://github.com/beshu-tech/deltaglider_proxy/issues).
+>
+> The stderr deprecation notice can be suppressed with
+> `DG_SUPPRESS_DEPRECATION=1` for CI that hasn't migrated yet.
+
+---
+
 [![PyPI version](https://badge.fury.io/py/deltaglider.svg)](https://pypi.org/project/deltaglider/)
 [![GitHub Repository](https://img.shields.io/badge/github-deltaglider-blue.svg)](https://github.com/beshu-tech/deltaglider)
 [![MIT License](https://img.shields.io/badge/license-MIT-blue.svg)](LICENSE)