Add CHANGELOG.md

Seed a changelog in the socket-python-cli format, starting at 3.4.3,
with a pointer to GitHub releases for earlier history.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Signed-off-by: lelia <2418071+lelia@users.noreply.github.com>

Author: lelia

CHANGELOG.md

@@ -0,0 +1,18 @@
+# Changelog
+
+## 3.4.3
+
+### Changed: bound runtime dependency ranges and pin build backend
+
+- Added version bounds to the runtime dependencies: `requests>=2.32.5,<3`
+  (previously unbounded) and `typing-extensions>=4.12.2,<5` (previously no
+  upper bound). As a library, socketdev declares bounded ranges rather than
+  exact pins so its constraints compose with consumers that pin their own
+  dependencies, such as the Socket Python CLI.
+- Pinned the `hatchling` build backend used for sdist builds.
+
+---
+
+Releases prior to 3.4.3 predate this changelog. See the
+[GitHub releases](https://github.com/SocketDev/socket-sdk-python/releases)
+for earlier release notes.