feat: iOS NucleusFont string initializer

ios/Sources/NucleusFonts/NucleusFont+Defaults.swift

@@ -170,3 +170,30 @@ public extension NucleusFont {
         dynamicTypeStyle: .caption2
     )
 }
+
+extension NucleusFont {
+    // map for token-string resolution
+    static let tokenDefaults: [String: NucleusFont] = [
+        "d1": .d1,
+        "n1": .n1,
+        "n2": .n2,
+        "n3": .n3,
+        "n4": .n4,
+        "n5": .n5,
+        "h1": .h1,
+        "h2": .h2,
+        "h3": .h3,
+        "h4": .h4,
+        "s1": .s1,
+        "s2": .s2,
+        "s3": .s3,
+        "s4": .s4,
+        "l1": .l1,
+        "l2": .l2,
+        "l3": .l3,
+        "b1": .b1,
+        "b2": .b2,
+        "b3": .b3,
+        "b4": .b4,
+    ]
+}

ios/Sources/NucleusFonts/NucleusFont.swift

@@ -50,6 +50,23 @@ public struct NucleusFont: Equatable, Hashable, Sendable {
     }
 }
 
+// MARK: - Token Resolution
+
+extension NucleusFont {
+    /// Resolves a token string like `"n2"` into its matching Nucleus font.
+    ///
+    /// Returns `nil` if the token doesn't map to a known default. In debug builds an unknown token also trips an assertion failure, so a stale or mistyped token surfaces during development rather than silently falling through.
+    ///
+    /// - Parameter token: The token string to resolve, e.g. `"n2"`.
+    public init?(token: String) {
+        guard let font = Self.tokenDefaults[token] else {
+            assertionFailure("unknown NucleusFont token: \(token)")
+            return nil
+        }
+        self = font
+    }
+}
+
 // MARK: - Mutating Methods
 
 extension NucleusFont {

tokens/templates/ios/NucleusFont+Defaults.swift.hbs

@@ -12,3 +12,12 @@ public extension NucleusFont {
     )
 {{/each}}
 }
+
+extension NucleusFont {
+    // map for token-string resolution
+    static let tokenDefaults: [String: NucleusFont] = [
+{{#each tokens}}
+        "{{name}}": .{{name}},
+{{/each}}
+    ]
+}