Create dockerfile and ci build task

[asg0451]

Add a Dockerfile, .dockerignore, and a CI workflow to build a multi-architecture Docker image for production readiness.

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[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
_{Learn more about Cursor Agents}

[github-actions]

Criterion benchmarks delta (ms; lower is better)

Benchmark	PR (ms)	Master (ms)	Δ (ms)	Δ (%)
e2e_rpc/rpc_add_batch_200	0.633	0.635	-0.002	-0.3%
e2e_rpc/rpc_poll_batch_200	48.086	47.725	0.361	+0.8%
e2e_rpc/rpc_remove_each_200	25.014	26.371	-1.357	-5.1%
e2e_rpc/rpc_stress_like_p2_a2_items_200	984.297	1002.413	-18.116	-1.8%
storage_add/add_available_500	8.041	8.051	-0.010	-0.1%
storage_poll/get_next_available_entries_500	11.251	10.993	0.258	+2.3%
storage_remove/remove_in_progress_500	19.440	19.538	-0.098	-0.5%