docs: App Store screenshot direction + screenshot tour UI test

[Ivan-LB]

Summary

• docs/plans/app-store-screenshots.md — the chosen direction for the App Store screenshots ("Seed to Sprout" on the notebook page), the eight-frame sequence with en-US / es-MX copy, the alternatives considered, the prerequisites found in the repo (es-419 gaps + hard-coded literals on the frames we show, the Config.plist/ATS/GoogleService-Info.plist truth gate for "No account. No cloud.", TARGETED_DEVICE_FAMILY = 1,2, dark mode via -darkModeEnabled YES, a seeded fictional dataset), and the production pipeline for the next session.
• SavelyUITests/StoreScreenshotTourUITests.swift — a screenshot tour (Home, Goals, Money, Me, "+" sheet, Log expense, scanner) that attaches full-resolution captures; the driver for real-screen artwork. Skipped on CI like the rest of SavelyUITests.
• Visual comps (5 frames at production coordinates, sprout stages, copy table): private artifact "Savely Storefront" — https://claude.ai/code/artifact/4fe9b96f-2879-4bd4-8d4b-3c3be30559f7

Why

Savely needs its own storefront identity — not Alisio's bands, Fingo's gradients or Thirds' cream editorial — and the research showed the "cream + serif" look is now the fintech default (Monarch/Matter). The growing SproutMark on a hairline rule is the one brand-native motif that is unmistakably Savely.

Test plan

• swiftlint --strict clean
• StoreScreenshotTourUITests runs green on the iPhone 17 Pro simulator (7 attachments)
• Nothing user-facing changes

Risks

None — docs + a UI test that is not run on CI.

Checklist

• Branch prefix docs/
• Conventional Commits
• No secrets staged