feat(rectification): remove the rectification regenerate button and endpoint (BUG-1056)

T2 of TASK-rectification-grounding-20260927 (product decision P1).
The rectification 「重试（重新生成）」 was a blind agent.generate rewrite that
persisted unchecked text (invented range / fit rate reproduced). Removed:
the regenerate route, regenerate-turn.ts, the regeneration agent and its
read-only tool set, the client regenerate action/state and the
regenerating/canRegenerate props. ChatMessageActions renders the regenerate
button only when onRegenerate is passed; ordinary consultation is unchanged.
The DB function regenerate_agentic_rectification_turn is kept (AGENTS §7.6,
retire in a later round). DESIGN.md / VOICE.md updated; source-contract
tests follow with 原值/新值/原因 notes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017eEAG8HD3mm8gsKXgk8uU8

frontend/tests/rectification-settled-render-split.test.ts

@@ -55,7 +55,6 @@ function emptyActions(): RectificationMessageEntryProps["actionsRef"] {
     submitChoice() {},
     submitStop() {},
     copyMessage() {},
-    regenerateMessage() {},
     onFeedback() {},
   };
   return actionsRef;
@@ -63,7 +62,7 @@ function emptyActions(): RectificationMessageEntryProps["actionsRef"] {
 
 function sharedProps(): Omit<
   RectificationMessageEntryProps,
-  "message" | "regenerating" | "canRegenerate" | "copied" | "feedback"
+  "message" | "copied" | "feedback"
 > {
   return {
     busy: true,
@@ -79,13 +78,12 @@ function sharedProps(): Omit<
 
 function entryProps(
   message: RenderMessage,
-  extras: Partial<Pick<RectificationMessageEntryProps, "regenerating" | "canRegenerate" | "copied" | "feedback">> = {},
+  extras: Partial<Pick<RectificationMessageEntryProps, "copied" | "feedback">> = {},
 ): RectificationMessageEntryProps {
+  // 原值: 另传 regenerating / canRegenerate。新值: 不再有这两项。原因: BUG-1056 删除生时校正重新生成。
   return {
     ...sharedProps(),
     message,
-    regenerating: extras.regenerating ?? false,
-    canRegenerate: extras.canRegenerate ?? false,
     copied: extras.copied ?? false,
     feedback: extras.feedback,
   };
@@ -140,10 +138,8 @@ test("the split architecture renders settled rectification rows once while strea
     renderToString(createElement(UnsplitRectificationMessageList, {
       ...shared,
       messages: [...history, liveAssistant(streamingText)],
-      latestRegeneratableKey: "a2",
       copiedMessageKey: null,
       feedbackByKey,
-      regeneratingMessageKey: null,
     }));
   }
   const unsplit = homeStreamingRenderProbeSnapshot();