0.2.0 - Playfair and six palettes

Typography and colour, plus the lock-flow fixes that were still sitting uncommitted.

Added

• Playfair Display bundled as five static TTFs (SIL OFL 1.1). Applied to display type only: screen titles, card titles, hero and giant timers, metric values, whispers, and Material display/headline/titleLarge.
• Three new accent schemes: Amber, Violet and Teal, alongside Blue, Green and Red. Settings now wraps the swatch row, so six fit without overflowing.

Changed

• Each accent scheme owns its whole page wash. canvasMid and canvasBottom were hardcoded blue; they now come from the scheme.
• Card surfaces are derived from the scheme's own wash instead of fixed blue-grey, so Amber no longer renders blue-grey cards on a warm canvas.
• Timers moved from Light to Normal weight, because Playfair has no Light.
• Seven hardcoded 20-22sp headings that bypassed the type tokens were brought onto the serif.

Fixed

• Starting a session no longer requires nothing: it now requires a key, and the same key ends it. With nothing armed the primary button reads "Scan key to start".
• Scanning an already-registered code always reported it as unregistered. The lookup read a WhileSubscribed(5000) flow whose cached value is empty when nothing collects it; it now hits the repository directly.
• Ending a session no longer lands on a blank page. stopSession was resetting the engine to Idle, which fired the overlay's back-navigation while the caller also popped, double-popping the hub.
• The session summary now reports duration and topic, and the hub's Stop always routes through it so it cannot be skipped.
• Cancelling during arming no longer leaves the engine in a stale Failed state.