Ongoing notification v2: expandable Now / Average breakdown (follow-up to #192)

[almothafar]

Follow-up to #192, which made the ongoing notification's title the stable headline (85% · Discharging) and the content line the volatile details. This is the agreed v2 shape (mockup-approved): make it expandable, and add a labelled Now / Average breakdown when pulled down.

Collapsed (the glance)

• Title (unchanged from Ongoing notification: stable metrics in the title, volatile details in the body #192): 85% · Discharging / 85% · Charging — stable metrics only.
• Content: 9%/h · −250 mA · ~9h 27m remaining while discharging, ~18 W · +1500 mA · ~45m to full while charging.
  • Adds the instantaneous current (mA) next to the rate (AccuBattery-style pairing).
  • Temperature moves to the expanded view to keep the collapsed line short.
  • Wording: "left" → "remaining" (matches the details table's "Time remaining").

Expanded (pull down)

Labelled lines, label — value:

Discharging

Now        −250 mA · 9%/h
Average    −338 mA · 5.9%/h
Remaining  ~9h 27m
Temp       34.6 °C

Charging

Now        +1500 mA · ~18 W
To full    ~45m
Temp       34.6 °C

• Now = the instant reading; Average = the windowed average (BatteryRate.avgCurrentMilliAmps, already computed for Current row flickers and disagrees between surfaces — show moment value with windowed average, gate visibility on the average #173).
• Discharging pairs mA with %/h; charging pairs mA with watts.

Notes

• Expandable = switch the ongoing notification from a single line to BigTextStyle (or a two-state layout). It's single-line today.
• Data: everything here already exists — %/h, instant + average mA, charge wattage, time estimates, temperature. No new tracking. (The Screen-on / Screen-off split is the separate Screen-on vs screen-off drain breakdown (notification + details table) #193.)
• New strings (EN + AR): Now, Average, Remaining, To full; rename the Ongoing notification: stable metrics in the title, volatile details in the body #192 %s left → %s remaining.
• Arabic / RTL: apply BidiFormatter (bidi isolation) to the collapsed detail line so the Latin values (−250 mA, %/h) don't reorder inside the RTL line — that was garbled without it. New labels: الآن / المتوسط / المتبقّي / الحرارة (drafted, pending maintainer review). The status word stays تستهلك.

Acceptance criteria

• Ongoing notification expands to the Now / Average / Remaining / Temp breakdown; collapses to the one-line glance
• Collapsed line shows rate · current · remaining (discharging) / watts · current · to-full (charging); temperature only in the expanded view
• "remaining" wording throughout (no "left")
• Arabic detail line is bidi-isolated and readable RTL; new labels in values-ar
• No new device reads — reuses the snapshot + rate the tick already computed (One snapshot per broadcast: derive ChargeSpeed from the BatteryDO in hand instead of fresh hardware reads #157)
• Robolectric coverage for the collapsed line and the expanded lines (discharging + charging), mirroring OngoingStatusLines

Related: #192 (v1), #193 (screen-on/off split, later), #108/#124/#173/#188.