fix(ios): keep tab screens hidden until their stack is sized

[samuelloranger]

Problem

On a cold launch, and on the first visit to a tab, screens drew a squeezed layout for a few frames before snapping to full width. Home's hero title wrapped word by word and the Pipeline card stacked one letter per line. Find showed "No results for these filters" in a narrow column, fading into the grid. #348 removed the crossfade that had been blurring these frames together, so they became more visible.

Measuring the layout showed the cause: the tab container is full size from the first frame, but the navigation stack inside it hands its root a zero-size proposal for its first ~0.3 s. SwiftUI lays the content out against that and draws it.

Changes

• Each tab root stays invisible until its navigation stack reports a real size (hiddenUntilSized(), applied in RootTabsView.tabRoot).
• Find shows its skeleton until its first load settles instead of the "no results" state, and its empty and error states take the full width.
• The Continue card paints its saved copy before the first frame. Painting it after the first frame, animated, slid Home's Pipeline card across it.
• A DEBUG simulator launch with RAWKOON_SERVER and RAWKOON_TOKEN now signs in before the first frame, so it reproduces a signed-in device launch. Previously it passed through Login, which hid the bug on the simulator.

Verification

• Recorded cold launches and first tab visits on the simulator against a live server before and after, and checked them frame by frame: no zero-size frames, no overlap between the Continue and Pipeline cards, no "no results" flash in Find.
• iOS check scripts, swiftformat --lint, and swiftlint (no errors).
• macbuild build and full test run passed.
• Installed on a physical device for a hands-on check.