refactor(P21): rename acdl_platform/ -> core/ (REQ-53)

---ci---
project: acdl
phase: 21
milestone: v1.6
status: execute
---/ci---

Rename the acdl_platform/ package to core/ across the directory, all
imports in tests/scripts/pipelines/workflows, and doc references. The
package is imported as core.confidence_signal / core.contract_resolver /
core.outbox_writer. The deploy workflow's platform-repo checkout dir is
renamed acdl-platform/ -> platform/ (workspace path, not the python
package). Both .gitea + .github workflows stay byte-identical.

Note: the original target name 'platform/' shadows Python's stdlib
platform module (pytest's import uuid -> platform.system() fails when
the repo root is on sys.path, which every test does). 'core/' avoids
the clash while honoring the intent (drop the verbose acdl_platform).

Tests: 154 pass. run_ci.sh green.

.github/workflows/deploy.yml

@@ -17,7 +17,7 @@
 #
 # What this workflow does:
 #   1. Checks out the consumer repo (the repo that invoked the workflow).
-#   2. Checks out the ACDL platform repo into the workspace (acdl-platform/).
+#   2. Checks out the ACDL platform repo into the workspace (platform/).
 #      This is the run-time fetch — consumers never clone the platform repo.
 #   3. Installs runtime deps: Python 3.12, Terraform 1.9.*, Checkov.
 #   4. Configures AWS auth (OIDC default; static-key override via secrets).
@@ -73,7 +73,7 @@ jobs:
         uses: actions/checkout@v4
         with:
           repository: acdl/acdl
-          path: acdl-platform
+          path: platform
           ref: v1.4
 
       - uses: actions/setup-python@v5
@@ -110,18 +110,18 @@ jobs:
             check-only) MODE_FLAG="--check-only" ;;
             *) echo "Unknown mode: ${{ inputs.mode }}"; exit 1 ;;
           esac
-          bash acdl-platform/scripts/run_platform.sh $MODE_FLAG "${{ inputs.contract }}"
+          bash platform/scripts/run_platform.sh $MODE_FLAG "${{ inputs.contract }}"
 
       - name: Upload emitted Terraform
         uses: actions/upload-artifact@v4
         with:
           name: acdl-terraform
-          path: acdl-platform/terraform/spike/*.tf
+          path: platform/terraform/spike/*.tf
           if-no-files-found: warn
 
       - name: Upload platform log
         uses: actions/upload-artifact@v4
         with:
           name: acdl-platform-log
-          path: acdl-platform/logs/
+          path: platform/logs/
           if-no-files-found: warn