chore: gitignore docker-compose.override.yml

Compose convention is that override.yml is a per-developer file for
local-dev overrides (e.g., forwarding PICLOUD_DEV_MODE +
PICLOUD_DEV_INSECURE_KEY to the picloud container without
modifying the tracked docker-compose.yml).

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

.gitignore

@@ -19,6 +19,9 @@ Cargo.lock.bak
 .env.*
 !.env.example
 
+# Local-only docker-compose overrides (per-developer)
+docker-compose.override.yml
+
 # Local config overrides
 config.local.toml
 /data