feat: scroll page instead of nested content, Base UI primitives for scroll locking

[barvian]

Summary

• The app shell no longer traps scroll in a nested content pane. The document (html) is the scroller, with a stable gutter so locking overlays does not shift the page.
• Banner, sidebar, and topbar are sticky and share the banner's height, so chrome stays put while the page moves, including when the banner dismisses.
• Vibenet home and the faucet fill short viewports with flex instead of a 100vh calc.
• Modals and the mobile nav use Base UI Dialog, so focus trapping and document scroll lock work against html rather than a homemade overflow lock on body.
• Changelog filters are Base UI Select (outline Button trigger) on every breakpoint. The mobile filter sheet is gone.

Test plan

• Tall page (changelog, explorer): the document scrolls; sidebar and topbar stay put
• Short page (Vibenet home, faucet): the page still fills the viewport; faucet address chips sit at the bottom
• Dismiss the banner: sidebar and topbar follow it up
• Open the mobile menu: it slides in; the page behind it does not scroll; Escape closes it
• Create Transaction (account demo): focus stays in the dialog; the page behind it does not scroll; Escape / backdrop / Close dismiss it
• Changelog filters: dropdown is left-aligned to the trigger; Tab shows the button focus outline; picking a value filters the table
• Changelog on a narrow viewport: same filter pills, no bottom sheet
• Activity drawer still spans the content column with no horizontal scrollbar
• Check desktop and mobile banner placement (full-width above the shell vs below the fixed header)

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

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Project	Deployment	Actions	Updated (UTC)
omni-ui	Ready	Preview	Aug 26, 2026 7:19pm