revert(build): drop ineffective per-commit cache-bust (#219)

SOURCE_COMMIT isn't substituted into docker-compose build args by Coolify
(resolved to a constant "unknown"), so the cache-bust never fired. Removing the
dead ARG/RUN + compose arg. Web-only deploys use a Coolify force-rebuild instead.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker-compose.coolify.yml

@@ -15,9 +15,6 @@ services:
         - VITE_SENTRY_DSN=${VITE_SENTRY_DSN:-}
         - VITE_SENTRY_ENVIRONMENT=${VITE_SENTRY_ENVIRONMENT:-production}
         - VITE_SENTRY_RELEASE=${VITE_SENTRY_RELEASE:-}
-        # Per-commit cache-bust (see Dockerfile) — Coolify substitutes the SHA so
-        # every commit rebuilds the bundle instead of reusing a stale cached layer.
-        - SOURCE_COMMIT=${SOURCE_COMMIT:-unknown}
         - VITE_GOOGLE_ADS_ID=${VITE_GOOGLE_ADS_ID:-}
         - VITE_GOOGLE_ADS_SIGNUP_LABEL=${VITE_GOOGLE_ADS_SIGNUP_LABEL:-}
     environment: