feat(power): "Low refresh" hourly sync, a sub-option of Power saving - #1430

Adds a user-elected hourly background-offload cadence under Settings -> Power
saving, beside the existing battery threshold and "Pause HRV capture" levers.
Unlike the battery lever it is not charge-gated: once chosen, 60 min is the
BASE the other levers stretch from, at any strap charge.

Fewer periodic offloads means fewer reconnect bursts, which is the measured
WHOOP 4.0 drain mechanism (#1120/#1144) - a strap log from a 10.1.1 staging
build showed 52 periodic offloads in a session, 26 of them idle-timeout stalls,
each holding the link and re-connecting for little or no new data.

Composition: every lever now stretches from the low-refresh base with `max`, so
a lever can only make the cadence quieter, never restore a faster one the user
asked to slow down. The 5/MG empty-history stretch (45 min) and the low-battery
stretch (45 min) are both shorter than 60 min, so they become no-ops rather than
speed-ups. Default off; with the toggle off every existing path is byte-identical.

DELIBERATELY CADENCE-ONLY - the idea comes from @cbedsole03, whose version also
stretched the keep-alive 30s -> 300s and released continuous HRV capture. Both
are dropped here because they cost data rather than delaying it:

- The keep-alive tick is not just a ping: it re-arms the WHOOP 4 realtime burst
  (R10/R11) every cycle so streaming cannot lapse, and it evaluates the stall
  fuse, which is 120s on a 4.0. A 300s tick under-samples that fuse, so a
  stalled 4.0 link would sit stalled up to 5 min - prolonging exactly the
  reconnect churn this feature exists to reduce. `startKeepAlive` already
  documents that the battery gain there "rounds to nothing on a 30 s timer".
- Releasing continuous HRV capture drops dense beat-to-beat R-R while it is on,
  INCLUDING overnight, which is where that stream exists to be dense. Density
  not captured cannot be backfilled later, and it would silently override the
  user`s own Continuous-HRV-capture preference. "Pause HRV capture" (#477) and
  the #927 overnight window are the levers for that, and they stay in charge.

So the shipped feature delays sync into larger batches and loses nothing: the
strap banks to flash and only trims on our ack.
PARITY: the Android twin lands in the same PR — NoopPrefs.lowRefresh, the
WhoopBleClient LOW_REFRESH_BACKFILL_INTERVAL_MS/baseBackfillIntervalMs pair, the
same max() composition inside nextBackfillDelayMs, and the same sub-toggle inside
the Settings if(powerSaving) block. Both platforms apply on the NEXT re-arm
(matching each side's existing battery lever), so a sync in flight is never cut.
New copy localized de/es/fr/pl/pt-PT/zh on Android and de/es/fr/pl/pt-PT in the
iOS catalog.

Tests: LowRefreshCadenceTests (Swift) + LowRefreshCadenceTest (Kotlin) pin the
same five cases — base on/off, and the three composition cases (low-battery
lever, 5/MG empty-history stretch, unchanged default path).

Validation: full Android suite 4042 tests / 490 classes green (5 new);
compileFullDebugKotlin + processFullDebugResources + i18n --ci green. The Swift
half is app-target, so it is validated by app-build; note StrandTests do not run
in default CI, so the Swift twin of the cadence test is compile-checked there
rather than executed.