fix(onboarding): make Accept/Install reachable on small screens

[web3dev1337]

Summary

The dependency setup wizard had reachability bugs on short viewports (landscape phones, small laptops, resized windows): the I Agree button on the Terms screen — and the Install/Next buttons on every setup step — could be pushed below the visible viewport with no way to scroll.

Root causes

1. .onboarding-container used 100vh + overflow: hidden. On iOS Safari, 100vh includes the URL bar, so the container was larger than the actual visible viewport, and overflow: hidden clipped anything that overflowed.
2. .onboarding-welcome-card, .onboarding-legal-card, and .onboarding-step-card set min-height: clamp(min, vh, max) where the min clamp value (320–360px) was enforced even on viewports shorter than ~600px. Combined with header + footer + paddings, the action row was pushed past the bottom of the viewport — and the container would not scroll.
3. The body-level body.dependency-onboarding-active #dependency-setup-modal override had higher specificity than .onboarding-overlay, so any padding/overflow fix had to be applied at both selectors.

What changed

• 100vh → 100dvh everywhere (accurate mobile viewport)
• overflow: hidden → overflow-y: auto on the container + the body-active modal selector, with scrollbar-gutter: stable and overscroll-behavior: contain
• New @media (max-height: 800px) and (max-height: 600px) rules drop the decorative min-height clamps and tighten paddings/typography so the action row is reachable on 320–800px-tall windows
• align-items: flex-start on short viewports so the modal starts at the top and users can scroll down naturally
• Safe-area insets (env(safe-area-inset-*)) added to all overlay paddings for notched devices

Test plan

Tested with Puppeteer at 6 viewport sizes — every size passes (I Agree button is either initially in view or reachable via container scroll):

Viewport	Before	After
1920×1080 (desktop)	in-view	in-view
1280×600 (laptop short)	in-view (tight)	in-view
1024×500 (laptop short)	clipped, no scroll	scrollable, reachable
390×844 (iPhone portrait)	clipped, partial scroll	scrollable, reachable
844×390 (iPhone landscape)	clipped, no scroll	scrollable, reachable
667×375 (small landscape)	clipped, no scroll	scrollable, reachable

Manual:

• Launch dev orchestrator, clear localStorage, reload — Terms screen appears
• Resize window height to 500px, confirm I Agree button visible after natural scroll
• Proceed through Install step pages, confirm Next/Install buttons reachable on short viewports

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