feat(ios): add Target Strain Reached notification

[tigercraft4]

Fixes #593.

Problem

WHOOP's official app fires a "Target Strain Reached" celebratory notification the moment you hit your day's target Strain. NOOP has wind-down, battery, illness, inactivity, and scheduled morning/workout report notifications, but nothing for this.

Honest scope note

The official copy ("You've hit your target Strain of X for this activity!") implies a per-activity target from an undocumented proprietary model — NOOP has no visibility into that algorithm. This instead fires against the day's recovery-based optimal-Strain floor (`CoupledView.optimalStrainRange(recovery:).lowerBound`) — the one target NOOP can actually compute honestly — and the notification copy says "today", not "for this activity", so it never overclaims precision NOOP doesn't have.

What's added

• `StrainGoalNotifier` (new file): pure once-per-day crossing policy (`StrainGoalPolicy`, mirrors `BatteryAlertPolicy`'s structure) + a point-in-time notification post gated on live `UNUserNotificationCenter` authorization status — same safe pattern as `BatteryNotifier`/`IllnessNotifier` (not the old unconditional-schedule bug `WindDownNudge` had, fixed in fix(ios): request notification permission and surface denial for wind-down nudge #251).
• `AppModel`: `evaluateStrainGoal(_:)` hooked into the same `repo.$days` sink as `evaluateIllness`; uses `Repository.widgetAnchor` to resolve which row is "Today" (same source Today/widget/Live Activity already agree on).
• `BehaviorStore`: `strainGoalAlerts` toggle, default OFF — opt-in like every automation here.
• `AutomationsView`: new "Strain goal" card, mirrors the Illness card's request-authorization-on-enable pattern.

Scope

iOS/macOS only, 4 files (1 new). No BLE/protocol/schema change — reads the existing `DailyMetric.strain`/`.recovery` fields and the existing `optimalStrainRange` helper. Android is a tracked fast-follow once this shape is confirmed (noted in #593).

Testing

macOS `Strand` scheme builds clean (0 errors) — `xcodebuild -scheme Strand -destination 'platform=macOS'`. Full `NOOPiOS` scheme not run locally (missing watchOS SDK in my environment, same constraint as prior PRs).

[ryanbr]

Thank you for this — the architecture instinct here is spot on (pure once-per-day crossing policy mirroring BatteryAlertPolicy, opt-in default-OFF, request-authorization-on-enable like IllnessNotifier), and the honesty note about not claiming a per-activity target NOOP can't compute is exactly the right call.

Closing as superseded, though — this landed in parallel with #596/#597, which already shipped the same feature on iOS/macOS (StrainTargetNotifier + the "Strain target" Automations card, merged). That's the coordination's fault, not yours — you called your shot on #593 and delivered. Because #597 touched the same three files, this PR is now conflicting anyway.

Two substantive reasons the merged version is the one to keep, in case they're useful for future work:

1. Strain scale. DailyMetric.strain is stored 0–100 (Effort), but optimalStrainRange(...).lowerBound is on the 0–21 WHOOP axis. strain >= targetStrain here compares 0–100 against 0–21, so it fires at ~14% effort (almost immediately) and the body prints a 0–100 number labelled as WHOOP Strain. Add opt-in "optimal strain reached" notification — iOS/macOS twin (#593) #597 converts first via UnitFormatter.effortValue(strain, scale: .whoop) and compares like-for-like.
2. "Today" resolution. Repository.widgetAnchor carries back to yesterday's row when today has no recovery yet (its purpose is the widget's recovery-carry display), so on an unscored morning it would evaluate yesterday's strain/target as "today". Add opt-in "optimal strain reached" notification — iOS/macOS twin (#593) #597 uses repo.today + optimalStrainRange(nil) → nil → no fire, which gates until today is actually scored.
3. Minor: Add opt-in "optimal strain reached" notification — iOS/macOS twin (#593) #597 uses NOOP's own copy ("Optimal strain reached") rather than WHOOP's decompiled strings, per the clean-room point raised on Add "Target Strain Reached" notification (WHOOP-native feature, currently missing) #593.

None of this is a knock on the work — the two above are subtle and easy to miss. If you'd like to keep going on this feature, the Android side is still an open fast-follow (noted on #593): the merged iOS StrainTargetPolicy is pure and easy to twin in Kotlin, and that PR would be very welcome. Thanks again.

[tigercraft4]

Thanks for the catch — I lifted "Target Strain Reached" / "You've hit your target Strain of X" straight from the decompiled strings without registering that's expression, not an interop fact. That was a mistake for a clean-room project; noted for next time. Good call closing this in favor of #596/#597 — properly scoped (day-band target choice, per-pass gate, NOOP's own copy) and already shipped on both platforms.