feat: add EntryWarnings and VocabularyBuilder

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

Sources/SstData/VocabularyBuilder.swift

@@ -0,0 +1,19 @@
+import Foundation
+
+/// The short word list handed to the speech engine as context.
+public enum VocabularyBuilder {
+    /// Terms first (file order), then the unique right-hand sides of correction pairs; at most `maxTerms` words.
+    public static func build(from entries: [DictionaryEntry], maxTerms: Int = 24) -> [String] {
+        var out: [String] = []
+        var seen = Set<String>()
+        func add(_ word: String) {
+            let key = word.lowercased()
+            guard !word.isEmpty, !seen.contains(key) else { return }
+            seen.insert(key)
+            out.append(word)
+        }
+        for entry in entries { if case .term(let term) = entry.kind { add(term) } }
+        for entry in entries { if case .correction(_, let wrote) = entry.kind { add(wrote) } }
+        return Array(out.prefix(maxTerms))
+    }
+}