History audit: 7-day charts collapsed to the newest ~25 h (list_history LIMIT 2000) — /history now buckets the whole window

Live Pi: hours=168 returned exactly 2000 points from 09-06 04:49 to 09-07 05:50 — the newest 2000 samples at ~2 s cadence, so every 7-day view showed ~a day. Fix on feat/dashboard-v2: whole-window bucketing to max_points (mean, binaries rounded), max_points query param (default 720), hours up to 90 d; SPA passes the points it draws; 30 d range on the VPD chart. 7 new tests (test_history_ops.py), suite 338 green. Verify after hotpatch: Climate › 7 d shows the full week.