feat(web): implement complete workspace with themes, tabs, sidebar, and mobile

Transform CalcText from a single-document calculator into a full workspace
application with multi-document support, theming, and responsive mobile experience.

- Theme system: 5 presets (Light, Dark, Matrix, Midnight, Warm) + accent colors
- Document model with localStorage persistence and auto-save
- Tab bar with keyboard shortcuts (Ctrl+N/W/Tab/1-9), rename, close
- Sidebar with search, recent, favorites, folders, templates, drag-and-drop
- 5 templates: Budget, Invoice, Unit Converter, Trip Planner, Loan Calculator
- Status bar with cursor position, engine status, dedication to Igor Cassel
- Results panel: type-specific colors, click-to-copy, error hints
- Format toolbar: H, B, I, //, color labels with live preview toggle
- Syntax highlighting using theme CSS variables
- Error hover tooltips
- Mobile: bottom results tray, sidebar drawer, touch targets, safe areas
- Docker multi-stage build (Rust WASM + Vite + Nginx)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

_bmad-output/A-Product-Brief/project-brief.md

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+# CalcText — Simplified Product Brief
+
+**Date:** 2026-03-17
+**Type:** Brownfield — Workspace Evolution
+**Brief Level:** Simplified
+
+---
+
+## Project Scope
+
+CalcText is a cross-platform notepad calculator (Web, macOS, Windows) powered by a shared Rust calculation engine with 200+ unit conversions, 180+ fiat currencies, 50+ crypto, date/time math, and 50+ built-in functions.
+
+The web app is evolving from a single-document, two-column calculator into a **full workspace application** with:
+
+- **Multi-theme system** — Light, Dark, Matrix, and custom user-defined themes
+- **Tabbed documents** — Multiple calctext files open simultaneously
+- **File sidebar** — Left panel with folder organization, recent files, favorites, templates
+- **localStorage persistence** — Documents survive page reloads without backend
+- **Elevated results panel** — Richer, subtler result display
+
+**Platform strategy:** Web-first design. Once established, replicate the UX patterns to macOS (SwiftUI) and Windows (iced/Rust). The design must be portable — avoid web-only paradigms that don't translate to native.
+
+---
+
+## Challenge & Opportunity
+
+CalcText has a powerful engine trapped in a basic single-document UI. The current web app is functional but doesn't reflect the depth of what the engine can do, and doesn't invite users to stay.
+
+**The opportunity:** No competitor (Soulver, Numi, Numbr, PCalc) offers a true multi-document workspace with theming and file organization for calculations. CalcText can own this gap — becoming the app users open daily and live in, not just visit for a quick calculation.
+
+**The gap:** Current UI is a text editor with results. The vision is a professional workspace where calculations are organized, styled, and persistent.
+
+---
+
+## Design Goals
+
+### Functional
+- Multi-theme engine with preset themes and custom theme support
+- Tab bar for multi-document management
+- Collapsible file sidebar with tree view, folders, and templates
+- Document model with create, rename, delete, organize
+- localStorage persistence for all documents and preferences
+
+### Experience
+- Professional workspace feel — "VS Code/Notion for numbers"
+- Complete experience shipped as one coherent product, not incremental phases
+- Matrix theme as a brand differentiator and personality statement
+- Intuitive for first-time users, powerful for daily users
+
+### Business
+- Web-first design that establishes reusable UX patterns
+- Cross-platform portable design language
+- Foundation for future premium features (cloud sync, accounts, collaboration)
+
+---
+
+## Constraints
+
+### Technical (locked in)
+- React 19 + CodeMirror 6 + Vite 7
+- Rust WASM engine running in Web Worker
+- Custom CSS with CSS custom properties (no Tailwind, no shadcn)
+- PWA architecture (service worker, manifest, offline support)
+
+### Deferred (out of scope this phase)
+- User accounts and authentication
+- Cloud save and sync (Supabase planned)
+- Collaborative real-time editing (CRDT)
+- Shareable URL links
+- Embeddable widget
+
+### Cross-platform
+- Design patterns must translate to SwiftUI (macOS) and iced (Windows)
+- Avoid web-only interactions that don't port to native
+- Shared engine means consistent calculation behavior across platforms
+
+### Timeline & Budget
+- Flexible — no hard deadline
+- Stakes: enterprise/high — quality over speed
+
+---
+
+## Current State Reference
+
+See `01-brownfield-analysis.md` for complete codebase scan including:
+- All CSS custom properties and values
+- Component inventory and props
+- Responsive breakpoints and behavior
+- Accessibility audit
+- Cross-platform comparison (macOS vs Web)
+
+---
+
+_Created using Whiteport Design Studio (WDS) methodology_