Redesign top bar with dedicated round badge and centered combatant name

Replace the combined "Round N — Name" string with a three-zone flex layout:
left (prev button + R{n} pill badge), center (prominent combatant name with
truncation), right (action buttons + next button). Adds 13 unit tests
covering all user stories including layout robustness and empty state.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

specs/034-topbar-redesign/data-model.md

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+# Data Model: Redesign Top Bar with Dedicated Round and Turn Fields
+
+**Feature**: 034-topbar-redesign | **Date**: 2026-03-11
+
+## Summary
+
+No data model changes required. This feature is a purely presentational refactor of the `TurnNavigation` component. All data needed for the new layout already exists in the `Encounter` type:
+
+- `encounter.roundNumber` — displayed in the round badge
+- `encounter.combatants[encounter.activeIndex].name` — displayed as the centered combatant name
+- `encounter.combatants.length` — used to determine the no-combatants state
+
+## Existing Entities (no changes)
+
+- **Encounter**: Contains `roundNumber` (number), `activeIndex` (number), and `combatants` (array). Already passed to `TurnNavigation` as a prop.
+- **Combatant**: Contains `name` (string). Already accessed via `encounter.combatants[encounter.activeIndex]`.
+
+## Component Interface (no changes)
+
+The `TurnNavigationProps` interface remains unchanged:
+
+```
+encounter: Encounter
+onAdvanceTurn: () => void
+onRetreatTurn: () => void
+onClearEncounter: () => void
+onRollAllInitiative: () => void
+onOpenSourceManager: () => void
+```