Stamp welcome cards in, fade the scrim, and add a debug reset

[kyleve]

Summary

• Fade the welcome-card scrim during presentation and dismissal. Previously, the card's scale-and-offset transition also transformed the full-screen scrim.
• Keep the overlay mounted and transition its scrim and card independently. Replace the shared 0.62-second motion with a 0.3-second tilted stamp arrival and a 0.16-second lift-and-fade departure. Reduce Motion uses a 0.16-second fade, and later presentations restore accessibility focus.
• Add Reset Welcome Card beside the welcome-card toggle in Settings > Appearance, only in debug builds. It clears the saved welcome region so returning to Locations can show the card again, using the normal recording and location checks.
• Keep the reset disabled while welcome cards are off. Localize its title and instructions, include it in Settings search, and update all ten Appearance references.

Testing

• ./swiftformat --lint — passed.
• ./test --snapshots --only WhereUISnapshotTests/LocationsViewSnapshotTests — passed (1 suite), including architecture validation and rule tests.
• ./test --only WhereUITests/LocationWelcomeModelTests --only WhereUITests/SettingsSearchTests — passed (23 tests). The reset regression covers replaying the same region in the same model and preserving the disabled preference.
• ./test --only WhereUITests/WhereStylesheetTests --only WhereUITests/LocationWelcomeModelTests — passed (40 tests), including arrival, departure, scrim, and Reduce Motion token assertions.
• ./test --snapshots --no-generate --no-build --only WhereUISnapshotTests/AppearanceSettingsViewSnapshotTests — passed (1 suite, 10 reviewed references).
• ./sf-symbols --lint and ./xcstrings --lint — passed.
• git diff --check — passed.
• The snapshots verify settled layouts. Live motion review remains pending because Simulator is unavailable through the connected UI controls. The debug reset supports replaying the transition on-device.