glitchtip/glitchtip:6.1.6 ships neither wget nor curl (only python3), so the
existing `wget --spider http://localhost:8080/api/0/` healthcheck failed on a
missing binary → container reported unhealthy forever. (wget --spider also
HEADs /api/0/, which GlitchTip 405s — "Method Not Allowed" in logs.)
Replace with the canonical /_health/ endpoint (GET → 200) probed via the
built-in python3. Verified live: the exact CMD exits 0 in the running
container. Nothing depends_on glitchtip-web's health, so this only fixes the
false-unhealthy status (no startup gating change).