feat(FN-1226): add production Docker workflow

- Add a root .dockerignore to reduce build context and exclude local runtime state
- Add a multi-stage Dockerfile that builds the workspace, runs as non-root, and includes health checks
- Document Docker build/run usage, env vars, persistence, and quick-start commands in README and docs/docker.md
- Add Docker configuration tests in packages/cli/src/docker.test.ts to validate required image and docs expectations

.dockerignore

@@ -0,0 +1,29 @@
+# Dependencies
+node_modules/
+
+# Build output
+dist/
+*.tsbuildinfo
+coverage/
+
+# Local runtime/state directories
+.fusion/
+.hai/
+.worktrees/
+.pi/
+.kb/
+.fusion-backup/
+.fusion-backup-*/
+
+# Mobile platform artifacts
+packages/dashboard/ios/
+packages/dashboard/android/
+
+# VCS/editor/OS artifacts
+.git/
+.DS_Store
+.idea/
+.vscode/
+
+# Release metadata not needed in image build context
+.changeset/