feat(phase-15): add Test Catalog page, template instantiation, and auto-migration entrypoint (T-119, T-120, T-121)

T-119: TestCatalogPage with search, filters (source/platform/severity), template cards grid, and pagination

T-120: TestFromTemplateForm modal with pre-filled fields from template, required field validation, and redirect on creation

T-121: Integrate Available Test Templates section in TechniqueDetailPage with Run This Test buttons; fix missing testStateBadgeColors for new states

Also: add backend entrypoint.sh for automatic Alembic migrations + seed on container startup, add curl to Dockerfile for healthcheck

backend/entrypoint.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+set -e
+
+echo "=== Running Alembic migrations ==="
+alembic upgrade head
+
+echo "=== Seeding admin user ==="
+python -m app.seed
+
+echo "=== Starting uvicorn ==="
+exec uvicorn app.main:app --host 0.0.0.0 --port 8000 --reload