feat: add Docker deployment and Gitea Actions CI/CD

Add multi-stage Dockerfile, docker-compose with persistent volumes,
and Gitea Actions workflows for CI (lint/test/build) and releases
(tag, Docker image push, changelog). Support DATABASE_PATH env var
for configurable SQLite location to enable proper volume mounting.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.dockerignore

@@ -0,0 +1,10 @@
+node_modules
+dist
+gearbox.db*
+uploads/*
+!uploads/.gitkeep
+.git
+.idea
+.claude
+.gitea
+.planning