feat: tables & event-feed polish (ui-ux 05, closes the epic)

[ArthurBernard]

Summary

Implements leaf 05 (doc/dev/plans/ui-ux-overhaul/05-tables-polish.md), the last leaf of the ui-ux-overhaul epic:

• No-flicker refresh — Strategies (3s poll), Overview (KPI/positions/open-orders) and Orders (orders/fills) tables cache the last payload (JSON.stringify compare) and skip the DOM rebuild when unchanged; a table never rebuilds while document.activeElement sits inside it (e.g. an open mode <select>), deferring the "updated" stamp too since the visible rows aren't verified current in that case. Shared via a new tbRefreshGuard() helper in base.html.
• Order-status badges — Orders page + Overview open-orders render status as a colour-coded badge (muted for new/submitted/open, amber for partially_filled, green for filled, dimmed for cancelled, red for rejected), via a shared statusBadge() helper + .badge-status-* CSS in base.html. Covers the domain's actual OrderStatus values plus a few defensive synonyms.
• History-cap caption — the Orders page's Orders/Fills tables show a muted "showing the most recent 200 — older rows are not displayed" caption when a history read comes back at exactly the server's default ?limit=200 cap.
• Fills time — absolute YYYY-MM-DD HH:mm:ss visible, relative ("3m ago") on hover.
• Logs page — lines are stamped with the event's own server ts (leaf 01), a muted strategy chip appears when the frame names the emitting unit, and All/Orders/Fills/Logs filter chips + a min-level select (info/warning/error) apply to both incoming and already-buffered events (a raw ring buffer, re-rendered on filter change; 500-line cap kept).
• PnL page — the stats table gains a Return column (realised_pnl / v0 via tbFmt.pct, "—" when v0 isn't a non-zero finite number) and a muted starting-capital (v0) note. Y-axis money-formatted ticks were already in place from an earlier leaf.
• Legacy dashboard.html/app.js untouched — already consistent with leaf 02's formatting, no new features added there per spec.

Closes the ui-ux-overhaul epic: doc/dev/plans/ui-ux-overhaul/00-plan.md flips to status: done, the roadmap's "Dashboard UX overhaul" line is removed, and doc/dev/06-status.md gains a summary paragraph. The plan tree itself is left in place (archived locally after merge, per the repo's workflow).

Test plan

• python -m pytest — 1165 passed, 9 deselected (network E2E)
• ruff check trading_bot/ — clean
• ruff format --check trading_bot/ — clean
• mypy trading_bot/ — clean
• interrogate trading_bot/ — 100%
• Extended template smoke tests: badge CSS + statusBadge helper present on every page, history-cap caption nodes + text, Logs filter chips (data-type=) + min-level select, PnL Return column header + v0 note
• New server-side test proving /api/orders?history=true&limit=N caps to exactly N rows (the real payload shape the caption logic keys on)
• Manual smoke: rendered all five pages via TestClient and grepped for the new markup

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