Bundle EF migrations for deployment

[BenjaminMichaelis]

Database migrations currently run during web-app startup, so every replica can participate in schema updates as the app deploys. This change packages migrations with the release image and moves execution into a single manual Azure Container Apps Job before the web app is updated.

• Build a Linux x64 EF migration bundle into the image and remove migration execution from application startup.
• Before Dev and Prod app updates, update the migration job to the exact image being deployed, start an execution, and wait for that execution to succeed. A failed or timed-out migration stops the rollout.
• Document local migration commands, the required MIGRATION_JOB_NAME GitHub Environment variables, and the possibility of downtime for breaking or long-running migrations.

Infrastructure dependency: the matching job resource, environment outputs, and job-scoped deployment permissions are in the separate Azure Resource Management worktree/session. Merge those Terraform changes and set the Development and Production MIGRATION_JOB_NAME variables to dev_web_migration_job_name and prod_web_migration_job_name before relying on these workflow steps.

Validation: Release solution build and all 176 tests passed; the Linux bundle generated successfully; no pending EF model changes; workflow YAML, shell syntax, and diff checks passed. Docker image build and Terraform validation/tests were unavailable because Docker and Terraform are not installed in this environment.

Fixes: #1133