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

.env.example

@@ -6,6 +6,12 @@ HOST_PORT=8011
 # Optional: override the Anthropic model used for extraction
 ANTHROPIC_MODEL=claude-sonnet-4-6
 
+# Durable CSV copies of discovery questions + answers. The per-conversation
+# files live in QUESTIONS_DIR; QUESTIONS_MASTER_CSV is an append-only log of
+# every save/complete event across conversations. Both default under ./data.
+QUESTIONS_DIR=./data/questions
+QUESTIONS_MASTER_CSV=./data/questions_master.csv
+
 # Google OAuth (web client type). Register the redirect URI below as an
 # authorized redirect URI in the Google Cloud Console for this client.
 GOOGLE_CLIENT_ID=xxxx.apps.googleusercontent.com