Implement the 010-ui-baseline feature that establishes a modern UI using Tailwind CSS v4 and shadcn/ui-style components for the encounter screen

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

specs/010-ui-baseline/data-model.md

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+# Data Model: UI Baseline
+
+**Feature**: 010-ui-baseline | **Date**: 2026-03-05
+
+## Domain Entities (UNCHANGED)
+
+This feature makes no domain changes. The existing domain types are consumed as-is by the UI layer.
+
+### Combatant (read-only from UI perspective)
+
+| Field | Type | Notes |
+|-------|------|-------|
+| id | CombatantId (branded string) | Unique identifier |
+| name | string | Display name, editable inline |
+| initiative | number \| undefined | Sort order, editable inline |
+| maxHp | number \| undefined | Maximum hit points |
+| currentHp | number \| undefined | Current hit points (present when maxHp is set) |
+
+### Encounter (read-only from UI perspective)
+
+| Field | Type | Notes |
+|-------|------|-------|
+| combatants | readonly Combatant[] | Sorted by initiative descending |
+| activeIndex | number | Index of current turn's combatant |
+| roundNumber | number | Current round counter |
+
+## UI Component Model (NEW)
+
+These are adapter-layer visual components — not domain entities.
+
+### CombatantRow
+
+Renders a single combatant as a structured row with consistent column alignment.
+
+| Column | Content | Behavior |
+|--------|---------|----------|
+| Initiative | Number or placeholder | Text input with `inputmode="numeric"`, no spinners, direct typing only |
+| Name | Combatant name | Inline editable, click-to-edit. Truncates with ellipsis |
+| HP | currentHp / maxHp | Text inputs with `inputmode="numeric"`, no spinners, direct entry for both values |
+| Actions | Remove icon button | Compact icon (X or trash), tooltip on hover |
+
+**Numeric field styling**: All numeric inputs use `type="text"` with `inputmode="numeric"` to suppress browser spinners while showing the numeric keyboard on mobile. Initiative uses `6ch` width (1–2 digit values typical). HP fields use `7ch` width (supports up to 4-digit values like 1000). All use tabular numerals (`font-variant-numeric: tabular-nums`) for column alignment and centered text.
+
+**Visual states**:
+- Default row
+- Active row (highlighted background/border for current turn)
+- Editing state (inline input replaces display text)
+
+### ActionBar
+
+Groups primary encounter controls.
+
+| Element | Type | Behavior |
+|---------|------|----------|
+| Name input | Text input | Enter combatant name |
+| Add button | Primary button | Adds combatant to encounter |
+| Next Turn button | Secondary/outline button | Advances to next combatant |
+
+### EncounterHeader
+
+Displays encounter status.
+
+| Element | Content |
+|---------|---------|
+| Title | "Initiative Tracker" |
+| Status | Round number and active combatant name |
+
+### EmptyState
+
+Displayed when combatants list is empty.
+
+| Element | Content |
+|---------|---------|
+| Message | "No combatants yet" or similar |
+| Hint | Prompt to add first combatant |