feat: Add FileWatcher and loadFromString

- FileWatcher: Observa archivo para detectar cambios via mtime
  - Intervalo configurable entre verificaciones
  - reset() y updateMtime() para control manual
- loadFromString(): Carga config desde string (para defaults embebidos)
- Tests para ambas funcionalidades

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

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

src/zcatconfig.zig

@@ -806,6 +806,126 @@ const loadFn = load;
 /// Funcion save renombrada para evitar conflicto con metodo
 const saveFn = save;
 
+// =============================================================================
+// FILE WATCHER
+// =============================================================================
+
+/// Observa un archivo para detectar cambios (via mtime)
+///
+/// Uso tipico:
+/// ```zig
+/// var watcher = FileWatcher.init("config.txt", 1000);  // check cada 1s
+/// // En main loop:
+/// if (watcher.checkForChanges()) {
+///     // Recargar configuracion
+/// }
+/// ```
+pub const FileWatcher = struct {
+    path: []const u8,
+    last_mtime: i128 = 0,
+    check_interval_ms: i64 = 1000,
+    last_check: i64 = 0,
+
+    /// Inicializa un FileWatcher para el path dado
+    /// @param path: ruta del archivo a observar
+    /// @param check_interval_ms: intervalo minimo entre verificaciones (default 1000ms)
+    pub fn init(path: []const u8, check_interval_ms: i64) FileWatcher {
+        return .{
+            .path = path,
+            .check_interval_ms = check_interval_ms,
+        };
+    }
+
+    /// Verifica si el archivo ha cambiado desde la ultima verificacion
+    /// Respeta el intervalo minimo entre verificaciones
+    /// @return true si el archivo cambio, false si no o si hubo error
+    pub fn checkForChanges(self: *FileWatcher) bool {
+        const now = std.time.milliTimestamp();
+
+        // Respetar intervalo minimo
+        if (now - self.last_check < self.check_interval_ms) {
+            return false;
+        }
+        self.last_check = now;
+
+        // Obtener mtime del archivo
+        const stat = std.fs.cwd().statFile(self.path) catch {
+            return false;
+        };
+
+        const file_mtime = stat.mtime;
+
+        // Primera vez - guardar mtime inicial
+        if (self.last_mtime == 0) {
+            self.last_mtime = file_mtime;
+            return false;
+        }
+
+        // Verificar si cambio
+        if (file_mtime != self.last_mtime) {
+            self.last_mtime = file_mtime;
+            return true;
+        }
+
+        return false;
+    }
+
+    /// Reinicia el watcher (olvida el mtime anterior)
+    pub fn reset(self: *FileWatcher) void {
+        self.last_mtime = 0;
+        self.last_check = 0;
+    }
+
+    /// Fuerza actualizar el mtime sin detectar cambio
+    /// Util despues de guardar el archivo
+    pub fn updateMtime(self: *FileWatcher) void {
+        const stat = std.fs.cwd().statFile(self.path) catch return;
+        self.last_mtime = stat.mtime;
+    }
+};
+
+// =============================================================================
+// LOAD FROM STRING
+// =============================================================================
+
+/// Carga configuracion desde un string (util para defaults embebidos)
+/// Similar a load() pero sin leer archivo
+pub fn loadFromString(
+    comptime variables: []const ConfigVariable,
+    comptime ConfigType: type,
+    config: *ConfigType,
+    content: []const u8,
+) void {
+    const EngineType = Engine(variables, ConfigType);
+
+    // Parsear linea por linea (igual que load())
+    var lines = std.mem.splitScalar(u8, content, '\n');
+    while (lines.next()) |line| {
+        const trimmed = std.mem.trim(u8, line, " \t\r");
+        if (trimmed.len == 0) continue;
+        if (trimmed[0] == '#') continue;
+        if (trimmed[0] != '@') continue;
+
+        // Buscar separador ':'
+        const colon_pos = std.mem.indexOf(u8, trimmed, ":") orelse continue;
+        const key = std.mem.trim(u8, trimmed[0..colon_pos], " \t");
+        const after_colon = trimmed[colon_pos + 1 ..];
+
+        // Quitar comentario inline
+        const comment_pos = findCommentStart(after_colon);
+        const value_with_spaces = if (comment_pos) |pos|
+            after_colon[0..pos]
+        else
+            after_colon;
+        const value = std.mem.trim(u8, value_with_spaces, " \t");
+
+        // Aplicar el valor
+        EngineType.set(config, key, value) catch {
+            continue;
+        };
+    }
+}
+
 // =============================================================================
 // TESTS
 // =============================================================================
@@ -965,3 +1085,47 @@ test "ConfigResult toString" {
     const color_result = ConfigResult{ .color = Color.rgb(255, 0, 128) };
     try std.testing.expectEqualStrings("RGB(255,0,128)", color_result.toString(&buf));
 }
+
+test "FileWatcher init" {
+    const watcher = FileWatcher.init("test.txt", 500);
+    try std.testing.expectEqualStrings("test.txt", watcher.path);
+    try std.testing.expectEqual(@as(i64, 500), watcher.check_interval_ms);
+    try std.testing.expectEqual(@as(i128, 0), watcher.last_mtime);
+}
+
+test "loadFromString basic" {
+    const test_vars = [_]ConfigVariable{
+        .{
+            .name = "enabled",
+            .config_key = "@enabled",
+            .var_type = .boolean,
+            .default = "Si",
+            .description = "Test",
+        },
+        .{
+            .name = "count",
+            .config_key = "@count",
+            .var_type = .integer,
+            .default = "10",
+            .description = "Test",
+        },
+    };
+
+    const TestConfig = struct {
+        enabled: bool = true,
+        count: i32 = 10,
+    };
+
+    var config = TestConfig{};
+
+    const content =
+        \\# Comentario
+        \\@enabled: No
+        \\@count: 42  # inline comment
+    ;
+
+    loadFromString(&test_vars, TestConfig, &config, content);
+
+    try std.testing.expectEqual(false, config.enabled);
+    try std.testing.expectEqual(@as(i32, 42), config.count);
+}