Show intermediate enrichment progress

[stef-k]

Summary

• reduce each durable enrichment execution to at most 10 ordered candidates
• reuse the existing authenticated content-free SSE hint after every committed workflow checkpoint
• keep remaining work scheduled through the existing one-shot Quartz projection
• correct user guidance and documentation

Closes #554

Validation

• focused candidate-cap, worker checkpoint/SSE, endpoint/filter, and documentation tests: 49 passed
• existing client SSE coalescing tests
• dotnet build --no-restore
• LOC and Code Guard review
• git diff --check

Design

No polling, new endpoint, heartbeat expansion, event payload data, or provider-contact behavior was added. PostgreSQL remains authoritative and SSE remains best-effort presentation.