docs: add responsible monetization strategy for LogWeight

[Copilot]

LogWeight needs a monetization approach that fits a privacy-first, single-purpose utility: inexpensive, low-friction, and non-disruptive to fast weight entry. This change documents a pricing model that preserves the app’s core promise while creating a clear path to revenue.

• Monetization strategy

  • Adds docs/Monetization.md with a recommended launch model:
    • free core app
    • optional one-time supporter purchase
    • suggested entry price of $2.99
    • no ads, no subscriptions, no gating of Apple Health logging/history
  • Defines guardrails for placement and UX so monetization stays out of the entry flow and remains confined to Settings.

• Product and release docs alignment

  • Links the new strategy from README.md so the approach is visible alongside the app’s product/privacy positioning.
  • Updates docs/AppStoreMetadata.md with launch-model guidance to keep release planning consistent with the documented pricing strategy.

• Scope boundaries

  • Keeps all current core capabilities free: logging, history, platform entry surfaces, and basic settings.
  • Frames monetization around voluntary support and small non-essential acknowledgements instead of feature withholding.

- Recommended launch model: free download with an optional one-time `Support LogWeight` purchase in Settings.
- Price target: start around `$2.99`
- No subscription, no ads, and no paywall around Apple Health logging or history.