Persist discovery answers to CSV for reprocessing and recovery

Save each discovery conversation's prompts and answers to durable CSV
files (per-conversation + append-only master log) on both save and
completion, so answers survive an extraction error, can be re-fed to the
AI, and can be reviewed/resumed by the user.

- app/services/answer_store.py: canonical prompt list + atomic CSV writes,
  master append, and read-back helpers (DB stays system of record; CSV
  failures are logged, never fatal).
- discovery router: write CSV on /respond and /complete; new endpoints
  GET /answers, GET /answers.csv, POST /reprocess (shared extraction
  helper; locked profiles return 409).
- discovery.html: prefill/resume from saved answers after an error and a
  "Re-run analysis" button wired to /reprocess.
- scripts/reprocess_csv.py: offline CLI to re-run extraction from a CSV
  (print or --write-db).
- QUESTIONS_DIR / QUESTIONS_MASTER_CSV config, .gitignore, README, tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Dg6XWUwprmP5QCL18HxssY

app/schemas.py

@@ -24,6 +24,21 @@ class RespondResponse(BaseModel):
     status: str
 
 
+class AnswerItem(BaseModel):
+    prompt_key: str
+    prompt_title: str
+    answer: str = ""
+
+
+class AnswersResponse(BaseModel):
+    """The saved prompts and answers for a conversation, for review/resume."""
+
+    conversation_id: str
+    started_at: datetime
+    completed_at: Optional[datetime] = None
+    answers: list[AnswerItem] = []
+
+
 class Confidence(BaseModel):
     triad: Optional[str] = None
     type: Optional[str] = None