feat: show the battery temperature range since the last full charge

[almothafar]

Closes #260

The problem

The battery temperature is read on every broadcast but was never retained, so after the fact there
was no way to tell whether the battery brushed the alert threshold for a minute or spent the
afternoon there — and no sense of what a normal temperature looks like on your own device.

The change

A new Temperature Range card in Battery Insights showing the coldest and hottest reading, in
the user's display unit (reuses TemperatureUtils.format, so °C/°F and the Western-digit
convention are already handled).

The window

The range accumulates continuously and resets only when a charge completes. Plugging in,
unplugging and the clock do nothing.

• "Charge complete" is BATTERY_STATUS_FULL or a level of 100. The status alone misses devices
  whose charge cap stops them short of 100 %; the level alone misses OEMs that report full a tick
  early.
• The reset is edge-triggered through a fullSeen flag, so it fires once per completed charge and
  re-arms when the battery leaves the full state — otherwise sitting plugged in at full would wipe
  the range on every broadcast. Same fire-once-then-re-arm shape as the full-battery alert's
  fullNotified.

The tracker

BatteryTemperatureTracker holds a running min/max plus that flag in the backup-excluded
battery_transient prefs (another device's range says nothing about this one). Fed from
BatteryLevelReceiver.onReceive next to BatteryHealthTracker.recordBatteryState, so no new
polling. Pure fold/summarize helpers, mirroring BatteryCapacityTracker.

Two details worth flagging:

• Readings of exactly 0 are rejected. SystemService reads EXTRA_TEMPERATURE with a
  default of 0, so on a device that doesn't report a temperature every tick would look like a
  freezing battery.
• No sample count. It would change on every tick and defeat the save-on-change rule the other
  trackers follow; hasData flips once and after that only a genuinely wider range writes.

Other files

• values/strings.xml + values-ar/strings.xml — four new strings, kept in parity (the
  MissingTranslation lint gate passes).
• CONTEXT.md — a Temperature range glossary entry, since CLAUDE.md makes the glossary
  binding for UI and code wording.

Tests

New BatteryTemperatureTrackerTest covering the running range, the plausibility gate (0, out of
band, and leaving an existing range untouched), and the reset: a completed charge starts a fresh
range; staying at full does not keep resetting; leaving full re-arms; plug-in/unplug alone do not
reset; full-level-without-full-status and full-status-below-full-level both count.

testDebugUnitTest, lintDebug and assembleDebug all pass on this branch.

Manual verification

Not run — no device available in this environment. Worth checking on hardware:

1. The card reads "—" on a fresh install, then real min/max once a broadcast lands.
2. Switching the unit preference to Fahrenheit — both values should follow.
3. The card in Arabic (RTL) for wrapping.
4. Charging to full collapses the range to that moment and it widens again; sitting at full does
   not keep resetting it.

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