Restructure CI/CD pipelines into reusable composite actions

[Smartdevs17]

Context

11 GitHub Actions workflows have significant duplication (checkout, Node setup, caching, linting, testing). Maintenance cost is high and updates require touching all workflows.

Current Limitation/Problem

A change to the Node setup step requires updating all 11 workflows. Some workflows exceed 300 lines of YAML with copy-pasted blocks.

Expected Outcome

Reusable composite actions: setup-node, build-contracts, run-tests, deploy-service. Each workflow is a short orchestration file (<50 lines) composing these actions.

Acceptance Criteria

• setup-node composite action: checkout, Node setup, dependency caching, .env generation from secrets
• build-contracts composite action: Rust toolchain setup, Soroban CLI, WASM build, artifact upload
• run-tests composite action: Jest config, coverage thresholds, JUnit report output
• deploy-service composite action: Docker build, image push to registry, Helm deploy with rollback
• All 11 workflows refactored to <50 lines each using composite actions
• Local testing: actions testable with act CLI (nektos/act)
• Edge case: action version pinning with semantic version tags (v1.2.3)

Technical Scope

• .github/actions/setup-node/action.yml - reusable composite action
• .github/actions/build-contracts/action.yml - reusable composite action
• .github/actions/run-tests/action.yml - reusable composite action
• .github/actions/deploy-service/action.yml - reusable composite action
• .github/workflows/ - refactored all 11 workflows
• .github/workflows/test-actions.yml - integration test for all actions

[Emmo00]

@Emmo00 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I would love to work on this issue.

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[drips-wave]

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