fix: move punctuation logic to LLM - backend returns complete joined text

The frontend no longer does separator/punctuation logic. Both Maestro
modes (generate and complete) now simply setPrompt(result). The LLM
is instructed to return the user's exact words + continuation, properly
joined. This is the right layer for text joining decisions.

frontend/src/components/Generator.tsx

@@ -187,23 +187,8 @@ export default function Generator({ onGenerate }: Props) {
               <label className="text-xs text-kithara-muted">Prompt</label>
               <MaestroButton
                 prompt={prompt}
-                onResult={(result, mode) => {
-                  if (mode === 'complete') {
-                    // Append continuation to existing prompt
-                    setPrompt(prev => {
-                      const trimmed = prev.trimEnd()
-                      const endsWithPunct = /[.!?,;:]$/.test(trimmed)
-                      const startsLower = /^[a-z]/.test(result)
-                      // Already punctuated? Just space.
-                      // Flows naturally (lowercase)? Just space.
-                      // Otherwise: period + space for a new sentence.
-                      const separator = (endsWithPunct || startsLower) ? ' ' : '. '
-                      return trimmed + separator + result
-                    })
-                  } else {
-                    // Generate mode: replace empty prompt
-                    setPrompt(result)
-                  }
+                onResult={(_result, _mode) => {
+                  setPrompt(_result)
                   setError('')
                 }}
                 onError={(msg) => setError(msg)}
@@ -226,22 +211,7 @@ export default function Generator({ onGenerate }: Props) {
               <MaestroButton
                 prompt={Object.values(structuredPrompt).filter(Boolean).join(' ')}
                 structured={isPro}
-                onResult={(result, mode) => {
-                  if (mode === 'complete') {
-                    // Fallback: append to additional field
-                    setStructuredPrompt(prev => {
-                      const existing = prev.additional?.trim() || ''
-                      const endsWithPunct = /[.!?,;:]$/.test(existing)
-                      const startsLower = /^[a-z]/.test(result)
-                      const separator = (endsWithPunct || startsLower) ? ' ' : '. '
-                      return { ...prev, additional: existing + separator + result }
-                    })
-                  } else {
-                    // Generate: put in additional
-                    setStructuredPrompt(prev => ({ ...prev, additional: result }))
-                  }
-                  setError('')
-                }}
+                onResult={(_result, _mode) => { /* handled by onStructuredResult */ }}
                 onStructuredResult={(fields, mode) => {
                   // Structured mode: merge fields into structuredPrompt, preserving user edits
                   setStructuredPrompt(prev => ({