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>

calcpad-engine/src/types.rs

@@ -12,6 +12,8 @@ pub enum ResultType {
     DateTime,
     TimeDelta,
     Boolean,
+    Empty,
+    NonCalculable,
     Error,
 }
 
@@ -24,6 +26,8 @@ impl fmt::Display for ResultType {
             ResultType::DateTime => write!(f, "DateTime"),
             ResultType::TimeDelta => write!(f, "TimeDelta"),
             ResultType::Boolean => write!(f, "Boolean"),
+            ResultType::Empty => write!(f, "Empty"),
+            ResultType::NonCalculable => write!(f, "NonCalculable"),
             ResultType::Error => write!(f, "Error"),
         }
     }
@@ -168,6 +172,36 @@ impl CalcResult {
         }
     }
 
+    pub fn empty(span: Span) -> Self {
+        CalcResult {
+            value: CalcValue::Error {
+                message: "empty input".to_string(),
+                span: span.into(),
+            },
+            metadata: ResultMetadata {
+                span: span.into(),
+                result_type: ResultType::Empty,
+                display: String::new(),
+                raw_value: None,
+            },
+        }
+    }
+
+    pub fn non_calculable(span: Span) -> Self {
+        CalcResult {
+            value: CalcValue::Error {
+                message: "no expression found".to_string(),
+                span: span.into(),
+            },
+            metadata: ResultMetadata {
+                span: span.into(),
+                result_type: ResultType::NonCalculable,
+                display: String::new(),
+                raw_value: None,
+            },
+        }
+    }
+
     pub fn error(message: &str, span: Span) -> Self {
         CalcResult {
             value: CalcValue::Error {
@@ -186,13 +220,34 @@ impl CalcResult {
     pub fn result_type(&self) -> ResultType {
         self.metadata.result_type
     }
+
+    /// Returns true if this result is a computed value (not empty, non-calculable, or error).
+    pub fn is_calculable(&self) -> bool {
+        !matches!(
+            self.metadata.result_type,
+            ResultType::Empty | ResultType::NonCalculable | ResultType::Error
+        )
+    }
 }
 
 fn format_number(val: f64) -> String {
     if val == val.floor() && val.abs() < 1e15 {
         format!("{}", val as i64)
     } else {
-        format!("{}", val)
+        // Round to 10 significant figures to avoid f64 noise
+        let abs = val.abs();
+        let magnitude = if abs > 0.0 { abs.log10().floor() as i32 } else { 0 };
+        let precision = (10 - magnitude - 1).max(0) as usize;
+        let formatted = format!("{:.prec$}", val, prec = precision);
+        // Strip trailing zeros after decimal point
+        if formatted.contains('.') {
+            formatted
+                .trim_end_matches('0')
+                .trim_end_matches('.')
+                .to_string()
+        } else {
+            formatted
+        }
     }
 }