feat(layout): finalize p01 and p02 changes

Complete UI foundation and app layout implementation, stabilize container health checks, and archive both OpenSpec changes after verification.

openspec/changes/archive/2026-02-18-p01-ui-foundation/proposal.md

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+# Proposal: UI Foundation
+
+## Overview
+Establish the foundational UI building blocks for Headroom's layout system. This includes types, stores, icon library, and theme configuration that all subsequent UI changes will depend on.
+
+## Goals
+- Install and configure Lucide icons for Svelte
+- Create layout-related TypeScript types
+- Create layout/period stores for state management
+- Set up theme system (light/dark mode with persistence)
+- Define navigation configuration structure
+
+## Non-Goals
+- Creating visual components (done in p02-app-layout)
+- Building actual pages (done in p03+)
+- API documentation (done in p00-api-documentation)
+
+## Priority
+**HIGH** - Foundation for all UI changes (p02-p05 depend on this)
+
+## Scope
+
+### Icon Library
+- Install `lucide-svelte` package
+- Create icon usage patterns/documentation
+- Replace existing inline SVGs where applicable
+
+### Types
+- `SidebarState` - 'expanded' | 'collapsed' | 'hidden'
+- `NavItem` - label, href, icon, roles
+- `NavSection` - title, items, roles (for role-based visibility)
+
+### Stores
+- `layoutStore` - sidebar state, theme preference
+- `periodStore` - global month/period selection
+
+### Theme System
+- DaisyUI theme switching via `data-theme` attribute
+- Light mode default ("light" theme)
+- Dark mode option ("dark" theme)
+- Persistence to localStorage
+- Respect system preference on first visit
+
+### Navigation Configuration
+- Centralized navigation structure
+- Role-based visibility for admin section
+
+## Success Criteria
+- [ ] Lucide icons installed and working
+- [ ] Types defined and exported
+- [ ] Stores created with localStorage persistence
+- [ ] Theme toggle functional
+- [ ] Navigation config exported
+- [ ] All tests pass
+
+## Estimated Effort
+1-2 hours
+
+## Dependencies
+- None (foundation change)
+
+## Blocks
+- p02-app-layout
+- p03-dashboard-enhancement
+- p04-content-patterns
+- p05-page-migrations