Add Docker support

Docker configuration:
- Dockerfile: Multi-stage build with non-root user, health checks
- Dockerfile.migrations: Runs EF Core migrations on startup
- docker-compose.yml: Full stack with SQL Server, Azurite, app
- .dockerignore: Optimized build context
- .env.example: Template for API keys

Application changes:
- Added /health endpoint with EF Core database check
- Conditional HTTPS redirect (disabled in containers)
- DOTNET_RUNNING_IN_CONTAINER environment detection

Usage:
  cp .env.example .env  # Add your API keys
  docker-compose up -d  # Start all services

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.dockerignore

@@ -0,0 +1,60 @@
+# Git
+.git
+.gitignore
+.gitattributes
+
+# Build outputs
+**/bin/
+**/obj/
+**/out/
+
+# IDE and editor files
+.vs/
+.vscode/
+.idea/
+*.user
+*.suo
+*.userosscache
+*.sln.docstates
+
+# Test results
+**/TestResults/
+**/coverage/
+
+# NuGet
+**/packages/
+
+# Documentation
+*.md
+!README.md
+
+# Docker files (don't need to copy these into the image)
+docker-compose*.yml
+Dockerfile*
+.dockerignore
+
+# Local settings (may contain secrets)
+**/appsettings.Development.json
+**/appsettings.Local.json
+**/*.local.json
+**/secrets.json
+
+# Environment files
+.env
+.env.*
+*.env
+
+# Logs
+**/logs/
+**/*.log
+
+# Temporary files
+**/tmp/
+**/temp/
+
+# OS files
+.DS_Store
+Thumbs.db
+
+# Tests (not needed in production image)
+tests/