feat: dashboard — last-evaluation per strategy + order timestamps

[ArthurBernard]

Summary

• Per-strategy "last point computed" — StrategyStatus (and /api/strategies) now carries last_eval_ts (wall-clock of the last tick attempt) and last_asof_ts (as-of of the last completed evaluation), read off PR fix: daemon tick performance — freshness gate + off-loop data loads #168's StrategyRunner/PortfolioRunner.last_eval_ms/last_asof_ms through the unit's runner. The Strategies table gains a Last eval column: relative time in the cell ("3m ago"), with the absolute evaluation instant and the as-of data date in title. Muted — before the first tick. Skipped on the Overview KPI rows (/api/kpi doesn't carry these fields and widening it is out of scope for this PR).
• Order date/time — every order row the dashboard API serves (/api/orders, both history=true and open) now carries ts (epoch ms, already the store's unit — no conversion needed). History rows read it straight off the store's ts column (a new SqliteStore.order_ts_map() bulk read — the domain Order itself carries no ts); open-order rows (sourced from the live router, which also carries no timestamp) look the same client_order_id up in the unit's store, null when not found. The Orders page's Orders table and the Overview's open-orders table both gain a Time column, mirroring the Fills table's exact formatting (absolute YYYY-MM-DD HH:mm:ss, relative time in title); order history now renders most-recent-first (mirroring how Fills already does).

Where ts comes from

Not the domain Order (it carries no timestamp) and not a per-row store lookup for history — a new SqliteStore.order_ts_map() (client_order_id -> ts, one query) feeds both order_history() and open_orders() via a new StrategySupervisor._order_ts_map_of(unit) helper that mirrors _stored_fills_of's dual read path (flush + read the live store when running, else a store opened at the unit's db_path).

Test plan

• python -m pytest — 1201 passed, 9 deselected
• ruff check trading_bot/ — clean
• ruff format --check trading_bot/ — clean
• mypy trading_bot/ — clean
• New tests: /api/strategies last_eval_ts/last_asof_ts null-before/set-after-tick; /api/orders history + open rows carry the right ts (incl. a "never persisted" id -> null); SqliteStore.order_ts_map() unit test; template smoke tests for the new column headers
• Manually verified end-to-end via a TestClient against a seeded paper supervisor (with and without a configured store) that ts/last_eval_ts/last_asof_ts populate correctly

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