feat: add Soroban contract CI pipeline and Kubernetes Helm chart (#917, #918)

[WhitesmokeX]

Summary

Closes #917 and #918.

#917 — Soroban Contract CI

Rewrites .github/workflows/contract-ci.yml with all required steps:

• cargo fmt --check — enforces consistent formatting
• cargo clippy -- -D warnings — zero lint warnings allowed
• cargo test + cargo test --features legacy-tests
• cargo build --target wasm32-unknown-unknown --release — WASM artifact uploaded
• All jobs have dedicated cargo registry + target cache keyed on Cargo.lock
• Triggers on push to main and PR targeting main (path-filtered to contract files)
• contract-ci gate job fails the workflow if any step above fails — set as required status check to block merges

#918 — Kubernetes Helm Chart

Adds charts/swiftremit/ — a production-grade Helm chart for all three services.

Templates:

Template	Resources
api-deployment.yaml	Deployment (api)
backend-deployment.yaml	Deployment (backend)
frontend-deployment.yaml	Deployment (frontend)
services.yaml	ClusterIP Services × 3
configmaps.yaml	ConfigMaps × 3 (non-secret env vars)
secrets.yaml	Secrets × 3 (stringData, injected at deploy time)
hpa.yaml	HorizontalPodAutoscaler for api + backend (+ frontend when enabled)
ingress.yaml	Optional nginx Ingress

Values files:

• values.yaml — base defaults
• values.dev.yaml — single replicas, testnet, in-cluster postgres
• values.staging.yaml — 2 replicas, testnet, staging cert-manager issuer
• values.production.yaml — 3+ replicas, mainnet, aggressive HPA, prod TLS

Deploy:

helm install swiftremit ./charts/swiftremit -f charts/swiftremit/values.production.yaml \
  --set api.secret.DATABASE_URL="$DATABASE_URL" \
  --set backend.secret.DATABASE_URL="$DATABASE_URL" \
  --set backend.secret.CONTRACT_ID="$CONTRACT_ID" \
  --set backend.secret.ADMIN_SECRET_KEY="$ADMIN_SECRET_KEY"

Helm lint CI: added helm-lint job to ci.yml — lints against all four values files, wired into the CI gate.

Testing

• helm lint charts/swiftremit — ✅ 0 failures across all four values files

closes #917
closes #918

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