Add EF Core storage query indexes

[mnbuhl]

Summary

• Adds provider-neutral EF Core indexes for hot Atomizer storage sweeps and lookups.
• Covers due jobs, partition heads, blocked partitions, leased-job recovery, idempotency lookup, due schedules, and stale heartbeat scans.
• Adds model metadata coverage so index names, column order, and uniqueness are locked down.

Changes

• Added composite indexes to the job, schedule, and active-server entity configurations used by AddAtomizerEntities.
• Kept provider SQL and storage behavior unchanged.
• Added configuration tests using EF model metadata inspection.

Risk and rollout

• Existing consumers that use migrations need to generate and apply an application migration after upgrading.
• Additional indexes increase write overhead, but reduce scan cost for common polling and recovery paths in larger tables.
• Rollback is to remove the generated consumer migration or downgrade the package.

[github-actions]

Package	Line Rate	Health
Atomizer	14%	❌
Atomizer.EntityFrameworkCore	91%	✔
Atomizer	14%	❌
Atomizer.EntityFrameworkCore	91%	✔
Atomizer	72%	➖
Atomizer	14%	❌
Atomizer.EntityFrameworkCore	91%	✔
Atomizer	72%	➖
Atomizer	72%	➖
Summary	60% (7471 / 13176)	➖