fix: smart separator respects existing punctuation

Don't add '.' if prompt already ends with punctuation (.!?,;:).
Logic: endsWithPunct || startsLower = just space, otherwise '. '
Prevents double-period '..' on continuation join.

frontend/src/components/Generator.tsx

@@ -192,10 +192,12 @@ export default function Generator({ onGenerate }: Props) {
                     // Append continuation to existing prompt
                     setPrompt(prev => {
                       const trimmed = prev.trimEnd()
-                      // If result starts lowercase, it flows from the input — just space
-                      // If result starts uppercase, treat as new sentence — period + space
+                      const endsWithPunct = /[.!?,;:]$/.test(trimmed)
                       const startsLower = /^[a-z]/.test(result)
-                      const separator = startsLower ? ' ' : '. '
+                      // Already punctuated? Just space.
+                      // Flows naturally (lowercase)? Just space.
+                      // Otherwise: period + space for a new sentence.
+                      const separator = (endsWithPunct || startsLower) ? ' ' : '. '
                       return trimmed + separator + result
                     })
                   } else {
@@ -229,8 +231,9 @@ export default function Generator({ onGenerate }: Props) {
                     // Fallback: append to additional field
                     setStructuredPrompt(prev => {
                       const existing = prev.additional?.trim() || ''
+                      const endsWithPunct = /[.!?,;:]$/.test(existing)
                       const startsLower = /^[a-z]/.test(result)
-                      const separator = startsLower ? ' ' : '. '
+                      const separator = (endsWithPunct || startsLower) ? ' ' : '. '
                       return { ...prev, additional: existing + separator + result }
                     })
                   } else {