Dashboard DISTINCT counts, equity/freshness panels, structured precursor events (fixes #224)

[wjllance]

Summary

Closes the four dashboard + log-pipeline gaps in issue #224.

1. DISTINCT counts — the Fills, Alerts, Cleanups, Cancel Reasons and Inventory Exits panels now use count(DISTINCT event_id) instead of count(*), matching the guidance in docs/15-openobserve.md. Daily duplicate uploads on network jitter (at-least-once retry) no longer inflate key metrics. The Cleanups metric also filters event='complete' so it is not skewed by the new retry-incomplete precursor rows.
2. New panels —
   • Equity / uPnL / Available trend (Overview), consuming cycle_summary.account (live runs only; account is null in paper mode).
   • Data Freshness (Overview) — max(_timestamp) + event count for the selected run.
   • Rejections & Error Signals (Runs & Events) — order/startup rejections, warning/critical risk notifications, and reconciliation/cleanup precursor failures.
   • Stream Health / Reconnects (Runs & Events) — order-response reconnect lifecycle by phase.
3. Structured precursor events — the two named precursor eprintln! signals now emit structured stdout JSON events in JSON mode (so the existing stdout ingest uploads them), while keeping the human-readable stderr line for non-JSON output, matching the existing emit_* pattern:
   • cancel-retry failures — recovery.rs, action=maker_cleanup, event=retry_incomplete, severity=warning.
   • reconciliation-snapshot failures — runtime.rs, action=position_reconciliation, event=snapshot_failed, severity=warning.
4. Ingest edge cases — checkpoints now record file identity (inode + size) and reset to zero on rotation/truncation; a corrupt state file auto-resets instead of wedging --follow at startup; and the checkpoint map is bounded via LRU eviction so openobserve-uploaded.json no longer grows unbounded. event_id idempotency remains the dedup safety net. Legacy int-valued state entries are still honored.

The STANDX_ENABLE_LIVE_MAKER live lock is untouched.

Test plan

• cargo fmt -- --check, cargo clippy --workspace --all-targets -- -D warnings, cargo test -p standx-cli — all green.
• python3 -m py_compile scripts/openobserve_dashboard.py scripts/openobserve_ingest.py scripts/test_openobserve_ingest.py.
• python3 -m unittest test_openobserve_ingest — 7 tests pass, including new coverage for truncation reset, corrupt-state auto-reset, legacy int state, and LRU bounding.
• Offline build_dashboard() smoke check: JSON-serializable, unique panel ids/layout indices per tab (Overview 13 panels, Runs & Events 7).

Fixes #224

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