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>

Dockerfile

@@ -0,0 +1,55 @@
+# Stage 1 — Build WASM from Rust
+FROM rust:1.85-bookworm AS wasm-builder
+
+# Install wasm-pack via pre-built binary (much faster than cargo install)
+RUN curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh
+
+WORKDIR /app
+
+# Copy workspace Cargo.toml
+COPY Cargo.toml ./
+
+# Copy the crates we actually need to compile
+COPY calcpad-engine/ calcpad-engine/
+COPY calcpad-wasm/ calcpad-wasm/
+
+# Create stub Cargo.toml + src for workspace members we don't need to build.
+# The workspace requires all members to exist, but we never compile these.
+RUN mkdir -p calcpad-cli/src && \
+    printf '[package]\nname = "calcpad-cli"\nversion = "0.1.0"\nedition = "2021"\n\n[[bin]]\nname = "calcpad"\npath = "src/main.rs"\n\n[dependencies]\ncalcpad-engine = { path = "../calcpad-engine" }\n' > calcpad-cli/Cargo.toml && \
+    echo 'fn main() {}' > calcpad-cli/src/main.rs && \
+    mkdir -p calcpad-windows/src && \
+    printf '[package]\nname = "calcpad-windows"\nversion = "0.1.0"\nedition = "2021"\n\n[[bin]]\nname = "calcpad-win"\npath = "src/main.rs"\n' > calcpad-windows/Cargo.toml && \
+    echo 'fn main() {}' > calcpad-windows/src/main.rs
+
+# Build WASM
+RUN wasm-pack build calcpad-wasm --target web --release
+
+# Stage 2 — Build frontend with Vite
+FROM node:22-slim AS web-builder
+
+WORKDIR /app/calcpad-web
+
+# Install dependencies first (layer caching)
+COPY calcpad-web/package.json calcpad-web/package-lock.json* ./
+RUN npm install
+
+# Copy web source
+COPY calcpad-web/ ./
+
+# Copy WASM output into public/wasm/ so Vite includes it in the build
+COPY --from=wasm-builder /app/calcpad-wasm/pkg/calcpad_wasm.js public/wasm/calcpad_wasm.js
+COPY --from=wasm-builder /app/calcpad-wasm/pkg/calcpad_wasm_bg.wasm public/wasm/calcpad_wasm_bg.wasm
+
+# Build (skip tsc type-check — that belongs in CI, not Docker)
+RUN npx vite build
+
+# Stage 3 — Serve with nginx
+FROM nginx:1.27-alpine
+
+COPY nginx.conf /etc/nginx/conf.d/default.conf
+COPY --from=web-builder /app/calcpad-web/dist /usr/share/nginx/html
+
+EXPOSE 8080
+
+CMD ["nginx", "-g", "daemon off;"]