fix(dashboardAPI): clean stat panels — dedup stray-tag series, value-only text, meter units

Three display defects surfaced when rendering the live PS/pump/MGC dashboards:

1. Doubled values everywhere. EVOLV telemetry historically carried stray tags
   (tagcode="undefined"/uuid="null") that newer writes dropped, so InfluxDB holds
   two series per field and last() returned two of everything (e.g. Time Left,
   Runtime, Heights). Add |> group(columns:["_field"]) before last()/aggregateWindow
   in every template query so each field collapses to one value/line regardless of
   tag-set history.

2. fields:"/.*/" also rendered the _time column as a stat value. For single-field
   string panels (Direction, Flow Source, Mode, State, Prediction Quality) append
   |> keep(columns:["_value"]); for mixed string+numeric panels (valve/vgc/monster)
   drop _time/_start/_stop instead.

3. Level/Heights showed "0.12 min" — Grafana unit id "m" means minutes, not meters.
   Change to lengthm; normalize m³->m3, m³/h->m3/h on pumpingStation.

Verified live via headless screenshots: PS, pump, and measurement dashboards now
show single clean values with correct units.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

config/settler.json

@@ -25,7 +25,7 @@
       "options": { "legend": { "displayMode": "list", "placement": "bottom" } },
       "targets": [
         {
-          "query": "from(bucket: \"${bucket}\")\n  |> range(start: v.timeRangeStart, stop: v.timeRangeStop)\n  |> filter(fn:(r) => r._measurement==\"${measurement}\")\n  |> filter(fn:(r) => r._field =~ /^(F_in|F_eff|F_so|F_sr|C_TS)/)\n  |> aggregateWindow(every: v.windowPeriod, fn: mean, createEmpty: false)",
+          "query": "from(bucket: \"${bucket}\")\n  |> range(start: v.timeRangeStart, stop: v.timeRangeStop)\n  |> filter(fn:(r) => r._measurement==\"${measurement}\")\n  |> filter(fn:(r) => r._field =~ /^(F_in|F_eff|F_so|F_sr|C_TS)/)\n  |> group(columns:[\"_field\"])\n  |> aggregateWindow(every: v.windowPeriod, fn: mean, createEmpty: false)",
           "refId": "A"
         }
       ],