feat(home): modular tile layout for the home page

[bilbospocketses]

What

Reworks the home page from the equal-height card grid into a modular tile grid: each category card sizes to its own content, and only data-heavy cards (Imaging Tools, Settings) grow to span two tile-units, lining up with the single cards stacked beside them. Also slims the hero into a compact band and left-aligns the card headers.

Why

The old grid stretched every card in a row to match the tallest one, so a one-link card (Android Devices) carried the same dead space as the six-link Imaging card. The tile layout keeps a uniform, aligned look while letting small cards stay small.

How

• Cards span var(--cm-tile-span) rows of a fixed tile-unit grid. The span is seeded server-side from the link count (close first paint, no flash), then measured-and-snapped to the exact value client-side, so any future card -- including 3- and 4-row ones -- just works.
• Measure-and-snap follows the app's existing window.controlMenu.* interop convention (the numeric-token resize pattern from sidebar-flyout.js), not ES modules -- theme.js documents why the app avoids those.
• Responsive: 3 roomy columns on a wide screen, falling back to 2 then 1 as the window narrows (content area widened to 1400px so 3 columns are not cramped).
• Colours come from the existing theme variables, so it works in light and dark.

Preserves module discovery, the Cameras-hidden-when-empty behaviour, the Settings card, the wizard gate, and pill rendering.

Test plan

• dotnet test -- 454 pass (adds HomeTileLayout.InitialSpan unit tests plus a bUnit span-seed assertion; existing Home tests stay green).
• Manual: verified in-browser at 1920px (3 columns, ~438px) and 1500px (2 columns), cards sizing to content (one-link = 1 unit, Imaging/Settings = 2 units), no clipping at any width.

Spec + plan: docs/superpowers/specs/2026-06-12-home-tile-layout-design.md, docs/superpowers/plans/2026-06-12-home-tile-layout.md.