feat(ui): inline large bar title on iPhone tab roots

[everpcpc]

What

• iPhone tab roots (Dashboard, Library, Offline, Search) now render a large serif title at the leading edge of the navigation bar row via ToolbarItem(placement: .largeTitle) + .toolbarTitleDisplayMode(.inlineLarge), gated to iOS 26+. The system hides the title on scroll down and restores it at the top by itself; the bar buttons stay put, and the bar background plus the top scroll-edge effect stay hidden so only the floating buttons remain. No system navigation title is set, so no collapsed bar title ever appears.
• Library picker moves to the trailing side on iPhone — on every page that shows it, tab roots and pushed browse pages alike — split from the ellipsis menu into its own capsule by a fixed ToolbarSpacer on iOS 26+ (on earlier iOS versions it also moves trailing, just without the spacer). Placement is unchanged elsewhere: leading (.cancellationAction) on iPad, .navigation on macOS.
• The Home tab is renamed to Dashboard (drops the now-unused tab.home localization key; macOS window title unchanged).
• Dashboard content no longer adds its own vertical padding — the taller inline-large bar provides the top spacing, and section bands already carry their own vertical rhythm. Title-to-first-section gap goes from 67pt to 51pt.

Why

The tab roots had no visible title on iPhone, and the library picker sat inside the trailing menu capsule. A leading large title gives each tab a clear identity in the bar row without spending content space on an in-content header, and the picker reads as its own control next to the menu.

Validation

• make build green on iOS, macOS, tvOS.
• iPhone 18 Pro simulator (iOS 27): all four tabs show the leading serif large title; scrolling down hides it while buttons stay, scrolling back restores it; no bar background or top blur; picker renders as a separate trailing capsule; pushed detail pages keep their normal bars.
• iPad Pro 13 simulator: no large title item, picker stays leading and opens correctly.
• make localize / translate.py list: no missing keys after removing tab.home.

Includes make bump to build 624.