refactor(P57): contract surface redesign + rename + .yml repo-wide

Contract surface redesign:
- New top-level fields: id (3-6 char acronym → stack.name), name (full → stack.title),
  infrastructure (map keyed by module name, replaces module:)
- Drop uses: field (dead reference; version pin lives in CI workflow uses: line)
- Drop top-level module/inputs (now nested under infrastructure map)
- Per-module optional version (defaults to latest published from registry)
- Multi-module contracts: one file deploys N modules in one pipeline run,
  resource IDs namespaced with module name to avoid collisions
- stack.schema.json: add optional title field for display name

Rename:
- pipelines/deploy.yaml → pipelines/contract.yml (declarative spec, not a pipeline)
- pipelines/ci.yaml → pipelines/ci.yml
- All 44 .yaml files → .yml repo-wide (contracts, module examples, kyverno policies)
- .acdl/contract.yaml → .acdl/contract.yml

Resolver (core/contract_resolver.py):
- Rewrite resolve() to loop infrastructure map, default version to latest,
  merge module fragments into one stack with namespaced resource IDs
- _latest_version() picks highest non-deprecated from registry
- _namespace_resources() prefixes IDs + rewrites ref: expressions for multi-module
- Single-module path: unprefixed IDs (backward compatible)

Verification:
- 494 tests pass (0 contract-shape failures)
- Local E2E passes (contract → resolver → adapter → local ECS HTTP 200 → outbox)

---ci---
project: acdl
phase: 57
milestone: v1.10.2
status: execute
---/ci---

.github/workflows/platform-test.yml

@@ -5,7 +5,7 @@
 #
 # Shell reproducibility: scripts/run_ci.sh runs lint + test + check-only locally.
 # The integration-test stage runs run_platform.sh --check-only for every
-# contracts/*.yaml file. The schema-validation stage validates schemas, module
+# contracts/*.yml file. The schema-validation stage validates schemas, module
 # interfaces, compositions, and example contracts.
 name: acdl-platform-test
 
@@ -62,7 +62,7 @@ jobs:
         run: pip install jsonschema pyyaml boto3
       - name: Run platform check-only for every sample contract
         run: |
-          for contract in contracts/*.yaml; do
+          for contract in contracts/*.yml; do
             echo "--- Testing $contract ---"
             bash scripts/run_platform.sh --check-only "$contract"
           done
@@ -139,7 +139,7 @@ jobs:
               except Exception as e:
                   print(f'{example}: SKIP (not a contract or invalid: {e})')
           # Also validate all sample contracts in contracts/
-          for contract_file in glob.glob('contracts/*.yaml'):
+          for contract_file in glob.glob('contracts/*.yml'):
               contract = yaml.safe_load(open(contract_file))
               jsonschema.validate(contract, schema)
               print(f'{contract_file}: valid contract')