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

[ryanbr]

Adds "Low refresh" as a sub-option of Settings → Power saving, beside the existing battery threshold and "Pause HRV capture" levers. Idea from @cbedsole03.

Unlike the battery lever it is not charge-gated: once chosen, 60 min becomes the BASE cadence the other levers stretch from, at any strap charge.

Why

Fewer periodic offloads means fewer reconnect bursts — the measured WHOOP 4.0 drain mechanism (#1120/#1144). A strap log from a 10.1.1 staging build showed 52 periodic offloads in one session, 26 of them idle-timeout stalls, each holding the link and reconnecting 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 (and why)

@cbedsole03's 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:

• Keep-alive: that tick is not just a ping — it re-arms the WHOOP 4 realtime burst (R10/R11) every cycle so streaming can't 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 minutes — 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."
• Continuous HRV capture: releasing it drops dense beat-to-beat R-R while on, including overnight, which is where that stream exists to be dense. Density not captured can't be backfilled later, and it would silently override the user's own Continuous-HRV-capture preference. "Pause HRV capture" ([ble] Battery: GATT connection-priority management (HIGH during offload/live, opt-in LOW_POWER idle) — Android #477) and the Count the packet types a history offload drops, instead of dropping them silently (#891) #927 overnight window remain the levers for that.

So what ships delays sync into larger batches and loses nothing: the strap banks to flash and only trims on our ack.

Parity

Android twin in the same PR — NoopPrefs.lowRefresh, the LOW_REFRESH_BACKFILL_INTERVAL_MS/baseBackfillIntervalMs pair, the same max() composition in 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 (Android) and de/es/fr/pl/pt-PT (iOS catalog).

Validation

• Full Android suite: 4,042 tests / 490 classes, 0 failures (5 new), plus compileFullDebugKotlin, processFullDebugResources (aapt) and i18n_audit.py --ci green.
• Swift half is app-target → validated by app-build. Note StrandTests don't run in default CI, so the Swift twin of the cadence test is compile-checked there rather than executed; the Kotlin twin pins the same five cases and does execute.