feat: historical BESS and NEM analytics platform

[djurcola-agent]

Scope

This draft preserves the accepted deployed BatteryWatch successor source and the in-progress historical analytics iteration on the djurcola-agent feature branch.

Accepted incremental slices currently include:

• database-backed API and independent five-minute Dispatch SCADA / DispatchIS collection;
• bounded NEMWeb archive planning and nested extraction using real reduced public fixtures;
• additive historical backfill run/item/event ledger migration;
• exact run creation/resume and interrupted-item recovery;
• deterministic concurrent-safe item claims using FOR UPDATE SKIP LOCKED with attempt/event history.

Verification at current head

• focused backfill ledger tests: 10 passed;
• full backend suite: 213 passed;
• Pyright: 0 errors, 0 warnings;
• Python compilation and git diff --check: passed;
• independent exact-hash review of the current claim tracer: passed with no findings.

Current state

This PR is intentionally draft and must not be merged yet. The current production deployment remains unchanged by the latest historical-backfill commits.

Still required before final acceptance:

• immutable archive artifact receipts and replay-safe completion/failure summaries;
• bounded archive downloader/runner and verified 30-day power/price backfill;
• authoritative per-DUID Next Day SOC plus separate regional BDU SOC;
• historical API/downsampling and estimate scenarios;
• dashboard historical controls/charts;
• full security/build/review gates, stateful backup, rollback-protected deployment, live database/browser acceptance, and two-interval stability proof.

No owner-main modification or merge is requested by this draft.