refactor: normalize script_builder_messages into separate table

Extract JSONB messages array from script_builder_sessions into a proper
script_builder_messages table with individual columns for role, content,
script, tokens, etc. Migration handles data migration from JSONB to rows.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/pages/ScriptBuilderPage.tsx

@@ -66,7 +66,7 @@ export default function ScriptBuilderPage() {
     const userMessage: ScriptBuilderMessage = {
       role: 'user',
       content,
-      timestamp: new Date().toISOString(),
+      created_at: new Date().toISOString(),
     }
     setMessages((prev) => [...prev, userMessage])
     setIsLoading(true)
@@ -88,7 +88,7 @@ export default function ScriptBuilderPage() {
         script: response.script,
         script_filename: response.script_filename,
         line_count: response.line_count,
-        timestamp: response.timestamp,
+        created_at: response.timestamp,
       }
       setMessages((prev) => [...prev, assistantMessage])
     } catch (err) {
@@ -96,7 +96,7 @@ export default function ScriptBuilderPage() {
       const errorMessage: ScriptBuilderMessage = {
         role: 'assistant',
         content: `An error occurred: ${err instanceof Error ? err.message : 'Failed to generate response. Please try again.'}`,
-        timestamp: new Date().toISOString(),
+        created_at: new Date().toISOString(),
       }
       setMessages((prev) => [...prev, errorMessage])
     } finally {

frontend/src/types/ai-session.ts

@@ -56,11 +56,11 @@ export interface ScriptBuilderContent {
   script_language?: string
 }
 
-export function isScriptGenerationAction(content: Record<string, unknown>): content is ScriptGenerationContent {
+export function isScriptGenerationAction(content: Record<string, unknown>): content is Record<string, unknown> & ScriptGenerationContent {
   return content.action_type === 'script_generation'
 }
 
-export function isScriptBuilderAction(content: Record<string, unknown>): content is ScriptBuilderContent {
+export function isScriptBuilderAction(content: Record<string, unknown>): content is Record<string, unknown> & ScriptBuilderContent {
   return content.action_type === 'open_script_builder'
 }
 

frontend/src/types/script-builder.ts

@@ -22,12 +22,15 @@ export interface ScriptBuilderSessionDetail {
 }
 
 export interface ScriptBuilderMessage {
+  id?: string
   role: 'user' | 'assistant'
   content: string
   script?: string | null
   script_filename?: string | null
   line_count?: number | null
-  timestamp: string
+  input_tokens?: number | null
+  output_tokens?: number | null
+  created_at: string
 }
 
 export interface ScriptBuilderMessageResponse {