fix: test suite sent real push notifications via the developer's .env

CHANGELOG.md

@@ -3,6 +3,13 @@
 All notable changes to this project will be documented here.
 Format follows [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+## [Unreleased]
+
+### Fixed
+- **The test suite sent real push notifications to the developer's phone.** `TestSyncCommand` invokes the actual `sync` command, which calls `load_config()`, which calls `load_dotenv()` — so the real `.env` was loaded and its live `NTFY_TOPIC` used for the POST. Every `pytest` run fired three or four pushes, including a fabricated "codex: 3 conversation(s) failed to export" straight out of a fixture, which is worse than noise: it reports a failure that never happened. Nothing appeared in `cache/logs/exporter.log` to explain it, because every test invocation passes `--no-log-file`.
+
+  A `tests/conftest.py` autouse fixture now neutralises the environment for every test: `NTFY_TOPIC`/`NTFY_TOKEN` are emptied, and `NTFY_SERVER` and `JOPLIN_API_URL` are pointed at a closed local port, so a stray topic cannot reach the internet and a test cannot write notes into a real Joplin instance. The values are **emptied rather than deleted** — `load_dotenv(override=False)` skips only keys already present, so deleting one lets `.env` put it back. Verified by instrumenting `requests` across a full run: zero outbound requests, where the same instrumentation without the fixture records POSTs to the live ntfy topic.
+
 ## [0.9.0] - 2026-08-18
 
 ### Fixed