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-request-dossier-cache.test.ts

@@ -27,7 +27,7 @@ const BARE_ADMIN_CLIENT = /accounting = createAdminSupabaseClient\(\)/;
 
 const CACHED_ROUTES = [
   "../src/app/api/rectification/agent/route.ts",
-  "../src/app/api/rectification/cases/[caseId]/turns/[turnId]/regenerate/route.ts",
+  // 原值: 含 cases/[caseId]/turns/[turnId]/regenerate/route.ts。新值: 移出。原因: BUG-1056（TASK-rectification-grounding-20260927 P1）删除生时校正的重新生成接口与按钮。
   "../src/app/api/rectification/cases/[caseId]/route.ts",
   "../src/app/api/rectification/cases/[caseId]/repair-exit/route.ts",
   "../src/app/api/rectification/cases/[caseId]/candidates/accept/route.ts",