feat: add calculator provider and frecency tracking

Calculator:
- Type "= expression" or "calc expression" for instant math evaluation
- Supports standard math functions (sqrt, sin, cos, etc.) and constants (pi, e)
- Copies result to clipboard on Enter via wl-copy

Frecency:
- Firefox-style algorithm: score = launch_count * recency_weight
- Boosts frequently and recently launched items in search results
- Persists to ~/.local/share/owlry/frecency.json
- Configurable via providers.frecency and providers.frecency_weight

New config options:
- providers.calculator = true
- providers.frecency = true
- providers.frecency_weight = 0.3

UI updates:
- Added :calc prefix support
- Calculator badge with yellow styling
- Updated hints to show "= calc" syntax

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/data/frecency.rs

@@ -0,0 +1,223 @@
+use chrono::{DateTime, Utc};
+use log::{debug, info, warn};
+use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
+use std::path::PathBuf;
+
+/// A single frecency entry tracking launch count and recency
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct FrecencyEntry {
+    pub launch_count: u32,
+    pub last_launch: DateTime<Utc>,
+}
+
+/// Persistent frecency data store
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct FrecencyData {
+    pub version: u32,
+    pub entries: HashMap<String, FrecencyEntry>,
+}
+
+impl Default for FrecencyData {
+    fn default() -> Self {
+        Self {
+            version: 1,
+            entries: HashMap::new(),
+        }
+    }
+}
+
+/// Frecency store for tracking and boosting recently/frequently used items
+pub struct FrecencyStore {
+    data: FrecencyData,
+    path: PathBuf,
+    dirty: bool,
+}
+
+impl FrecencyStore {
+    /// Create a new frecency store, loading existing data if available
+    pub fn new() -> Self {
+        let path = Self::data_path();
+        let data = Self::load_from_path(&path).unwrap_or_default();
+
+        info!("Frecency store loaded with {} entries", data.entries.len());
+
+        Self {
+            data,
+            path,
+            dirty: false,
+        }
+    }
+
+    /// Alias for new() - loads from disk or creates default
+    pub fn load_or_default() -> Self {
+        Self::new()
+    }
+
+    /// Get the path to the frecency data file
+    fn data_path() -> PathBuf {
+        dirs::data_dir()
+            .unwrap_or_else(|| PathBuf::from("."))
+            .join("owlry")
+            .join("frecency.json")
+    }
+
+    /// Load frecency data from a file
+    fn load_from_path(path: &PathBuf) -> Option<FrecencyData> {
+        if !path.exists() {
+            debug!("Frecency file not found at {:?}", path);
+            return None;
+        }
+
+        let content = std::fs::read_to_string(path).ok()?;
+        match serde_json::from_str(&content) {
+            Ok(data) => Some(data),
+            Err(e) => {
+                warn!("Failed to parse frecency data: {}", e);
+                None
+            }
+        }
+    }
+
+    /// Save frecency data to disk
+    pub fn save(&mut self) -> Result<(), Box<dyn std::error::Error>> {
+        if !self.dirty {
+            return Ok(());
+        }
+
+        // Ensure directory exists
+        if let Some(parent) = self.path.parent() {
+            std::fs::create_dir_all(parent)?;
+        }
+
+        let content = serde_json::to_string_pretty(&self.data)?;
+        std::fs::write(&self.path, content)?;
+        self.dirty = false;
+
+        debug!("Frecency data saved to {:?}", self.path);
+        Ok(())
+    }
+
+    /// Record a launch event for an item
+    pub fn record_launch(&mut self, item_id: &str) {
+        let now = Utc::now();
+
+        let entry = self
+            .data
+            .entries
+            .entry(item_id.to_string())
+            .or_insert(FrecencyEntry {
+                launch_count: 0,
+                last_launch: now,
+            });
+
+        entry.launch_count += 1;
+        entry.last_launch = now;
+        self.dirty = true;
+
+        debug!(
+            "Recorded launch for '{}': count={}, last={}",
+            item_id, entry.launch_count, entry.last_launch
+        );
+
+        // Auto-save after recording
+        if let Err(e) = self.save() {
+            warn!("Failed to save frecency data: {}", e);
+        }
+    }
+
+    /// Calculate frecency score for an item
+    /// Uses Firefox-style algorithm: score = launch_count * recency_weight
+    pub fn get_score(&self, item_id: &str) -> f64 {
+        match self.data.entries.get(item_id) {
+            Some(entry) => Self::calculate_frecency(entry.launch_count, entry.last_launch),
+            None => 0.0,
+        }
+    }
+
+    /// Calculate frecency using Firefox-style algorithm
+    fn calculate_frecency(launch_count: u32, last_launch: DateTime<Utc>) -> f64 {
+        let now = Utc::now();
+        let age = now.signed_duration_since(last_launch);
+        let age_days = age.num_hours() as f64 / 24.0;
+
+        // Recency weight based on how recently the item was used
+        let recency_weight = if age_days < 1.0 {
+            100.0 // Today
+        } else if age_days < 7.0 {
+            70.0 // This week
+        } else if age_days < 30.0 {
+            50.0 // This month
+        } else if age_days < 90.0 {
+            30.0 // This quarter
+        } else {
+            10.0 // Older
+        };
+
+        launch_count as f64 * recency_weight
+    }
+
+    /// Get all entries (for debugging/display)
+    #[allow(dead_code)]
+    pub fn entries(&self) -> &HashMap<String, FrecencyEntry> {
+        &self.data.entries
+    }
+
+    /// Clear all frecency data
+    #[allow(dead_code)]
+    pub fn clear(&mut self) {
+        self.data.entries.clear();
+        self.dirty = true;
+    }
+}
+
+impl Default for FrecencyStore {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl Drop for FrecencyStore {
+    fn drop(&mut self) {
+        // Attempt to save on drop
+        if let Err(e) = self.save() {
+            warn!("Failed to save frecency data on drop: {}", e);
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_frecency_calculation() {
+        let now = Utc::now();
+
+        // Recent launch should have high score
+        let score_today = FrecencyStore::calculate_frecency(10, now);
+        assert!(score_today > 900.0); // 10 * 100
+
+        // Older launch should have lower score
+        let week_ago = now - chrono::Duration::days(5);
+        let score_week = FrecencyStore::calculate_frecency(10, week_ago);
+        assert!(score_week < score_today);
+        assert!(score_week > 600.0); // 10 * 70
+
+        // Much older launch
+        let month_ago = now - chrono::Duration::days(45);
+        let score_month = FrecencyStore::calculate_frecency(10, month_ago);
+        assert!(score_month < score_week);
+    }
+
+    #[test]
+    fn test_launch_count_matters() {
+        let now = Utc::now();
+
+        let score_few = FrecencyStore::calculate_frecency(2, now);
+        let score_many = FrecencyStore::calculate_frecency(20, now);
+
+        assert!(score_many > score_few);
+        assert!((score_many / score_few - 10.0).abs() < 0.1); // Should be ~10x
+    }
+}