feat(owlry-core): move backend modules from owlry

Move the following modules from crates/owlry/src/ to crates/owlry-core/src/:
- config/ (configuration loading and types)
- data/ (frecency store)
- filter.rs (provider filtering and prefix parsing)
- notify.rs (desktop notifications)
- paths.rs (XDG path handling)
- plugins/ (plugin system: native loader, manifest, registry, runtime loader, Lua API)
- providers/ (provider trait, manager, application, command, native_provider, lua_provider)

Notable changes from the original:
- providers/mod.rs: ProviderManager constructor changed from with_native_plugins()
  to new(core_providers, native_providers) to decouple from DmenuProvider
  (which stays in owlry as a UI concern)
- plugins/mod.rs: commands module removed (stays in owlry as CLI concern)
- Added thiserror and tempfile dependencies to owlry-core Cargo.toml

crates/owlry-core/src/plugins/api/math.rs

@@ -0,0 +1,181 @@
+//! Math calculation API for Lua plugins
+//!
+//! Provides safe math expression evaluation:
+//! - `owlry.math.calculate(expression)` - Evaluate a math expression
+
+use mlua::{Lua, Result as LuaResult, Table};
+
+/// Register math APIs
+pub fn register_math_api(lua: &Lua, owlry: &Table) -> LuaResult<()> {
+    let math_table = lua.create_table()?;
+
+    // owlry.math.calculate(expression) -> number or nil, error
+    // Evaluates a mathematical expression safely
+    // Returns (result, nil) on success or (nil, error_message) on failure
+    math_table.set(
+        "calculate",
+        lua.create_function(|_lua, expr: String| -> LuaResult<(Option<f64>, Option<String>)> {
+            match meval::eval_str(&expr) {
+                Ok(result) => {
+                    if result.is_finite() {
+                        Ok((Some(result), None))
+                    } else {
+                        Ok((None, Some("Result is not a finite number".to_string())))
+                    }
+                }
+                Err(e) => {
+                    Ok((None, Some(e.to_string())))
+                }
+            }
+        })?,
+    )?;
+
+    // owlry.math.calc(expression) -> number (throws on error)
+    // Convenience function that throws instead of returning error
+    math_table.set(
+        "calc",
+        lua.create_function(|_lua, expr: String| {
+            meval::eval_str(&expr)
+                .map_err(|e| mlua::Error::external(format!("Math error: {}", e)))
+                .and_then(|r| {
+                    if r.is_finite() {
+                        Ok(r)
+                    } else {
+                        Err(mlua::Error::external("Result is not a finite number"))
+                    }
+                })
+        })?,
+    )?;
+
+    // owlry.math.is_expression(str) -> boolean
+    // Check if a string looks like a math expression
+    math_table.set(
+        "is_expression",
+        lua.create_function(|_lua, expr: String| {
+            let trimmed = expr.trim();
+
+            // Must have at least one digit
+            if !trimmed.chars().any(|c| c.is_ascii_digit()) {
+                return Ok(false);
+            }
+
+            // Should only contain valid math characters
+            let valid = trimmed.chars().all(|c| {
+                c.is_ascii_digit()
+                    || c.is_ascii_alphabetic()
+                    || matches!(c, '+' | '-' | '*' | '/' | '^' | '(' | ')' | '.' | ' ' | '%')
+            });
+
+            Ok(valid)
+        })?,
+    )?;
+
+    // owlry.math.format(number, decimals?) -> string
+    // Format a number with optional decimal places
+    math_table.set(
+        "format",
+        lua.create_function(|_lua, (num, decimals): (f64, Option<usize>)| {
+            let decimals = decimals.unwrap_or(2);
+
+            // Check if it's effectively an integer
+            if (num - num.round()).abs() < f64::EPSILON {
+                Ok(format!("{}", num as i64))
+            } else {
+                Ok(format!("{:.prec$}", num, prec = decimals))
+            }
+        })?,
+    )?;
+
+    owlry.set("math", math_table)?;
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn setup_lua() -> Lua {
+        let lua = Lua::new();
+        let owlry = lua.create_table().unwrap();
+        register_math_api(&lua, &owlry).unwrap();
+        lua.globals().set("owlry", owlry).unwrap();
+        lua
+    }
+
+    #[test]
+    fn test_calculate_basic() {
+        let lua = setup_lua();
+
+        let chunk = lua.load(r#"
+            local result, err = owlry.math.calculate("2 + 2")
+            if err then error(err) end
+            return result
+        "#);
+        let result: f64 = chunk.call(()).unwrap();
+        assert!((result - 4.0).abs() < f64::EPSILON);
+    }
+
+    #[test]
+    fn test_calculate_complex() {
+        let lua = setup_lua();
+
+        let chunk = lua.load(r#"
+            local result, err = owlry.math.calculate("sqrt(16) + 2^3")
+            if err then error(err) end
+            return result
+        "#);
+        let result: f64 = chunk.call(()).unwrap();
+        assert!((result - 12.0).abs() < f64::EPSILON); // sqrt(16) = 4, 2^3 = 8
+    }
+
+    #[test]
+    fn test_calculate_error() {
+        let lua = setup_lua();
+
+        let chunk = lua.load(r#"
+            local result, err = owlry.math.calculate("invalid expression @@")
+            if result then
+                return false -- should not succeed
+            else
+                return true -- correctly failed
+            end
+        "#);
+        let had_error: bool = chunk.call(()).unwrap();
+        assert!(had_error);
+    }
+
+    #[test]
+    fn test_calc_throws() {
+        let lua = setup_lua();
+
+        let chunk = lua.load(r#"return owlry.math.calc("3 * 4")"#);
+        let result: f64 = chunk.call(()).unwrap();
+        assert!((result - 12.0).abs() < f64::EPSILON);
+    }
+
+    #[test]
+    fn test_is_expression() {
+        let lua = setup_lua();
+
+        let chunk = lua.load(r#"return owlry.math.is_expression("2 + 2")"#);
+        let is_expr: bool = chunk.call(()).unwrap();
+        assert!(is_expr);
+
+        let chunk = lua.load(r#"return owlry.math.is_expression("hello world")"#);
+        let is_expr: bool = chunk.call(()).unwrap();
+        assert!(!is_expr);
+    }
+
+    #[test]
+    fn test_format() {
+        let lua = setup_lua();
+
+        let chunk = lua.load(r#"return owlry.math.format(3.14159, 2)"#);
+        let formatted: String = chunk.call(()).unwrap();
+        assert_eq!(formatted, "3.14");
+
+        let chunk = lua.load(r#"return owlry.math.format(42.0)"#);
+        let formatted: String = chunk.call(()).unwrap();
+        assert_eq!(formatted, "42");
+    }
+}