Fixes #35 — vocab practice no longer doubles the verb's "to"

VocabFlashcardPracticeView and VocabMultipleChoicePracticeView rendered
the English prompt as "to \(verb.english)". Every verb in conjuga_data
already stores english with a leading "to " (all 1750 of them), so the
prompt came out as "to to be", "to to run", etc.

Dropped the prefix — verb.english is shown verbatim. Same fix applied
to the Image Playground concept string so generated illustrations are
prompted with "to be" rather than "to to be".

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Conjuga/Conjuga/Views/Practice/Vocab/VocabFlashcardPracticeView.swift

@@ -68,7 +68,7 @@ struct VocabFlashcardPracticeView: View {
 
     @ViewBuilder
     private func cardBody(_ verb: Verb) -> some View {
-        Text("to \(verb.english)")
+        Text(verb.english)
             .font(.largeTitle.weight(.bold))
             .multilineTextAlignment(.center)
             .padding(.top, 12)
@@ -347,7 +347,7 @@ struct VerbIllustration: View {
         }
         guard VocabImageService.isAvailable else { return }
         isGenerating = true
-        let result = await service.image(forKey: cacheKey, concept: "to \(verb.english)")
+        let result = await service.image(forKey: cacheKey, concept: verb.english)
         isGenerating = false
         if let result {
             image = result

Conjuga/Conjuga/Views/Practice/Vocab/VocabMultipleChoicePracticeView.swift

@@ -63,7 +63,7 @@ struct VocabMultipleChoicePracticeView: View {
 
     @ViewBuilder
     private func questionBody(_ verb: Verb) -> some View {
-        Text("to \(verb.english)")
+        Text(verb.english)
             .font(.largeTitle.weight(.bold))
             .multilineTextAlignment(.center)
             .padding(.top, 12)