Harden the API and the data layer after a security and performance audit

Security
- Every route now requires a login and refuses ids outside the caller's
  workspace with 404: plan, leave-wishes, day-overrides and vacation-days
  were fully anonymous; every other router trusted client-supplied
  workspace/child/parent ids. Scraper sessions are bound to their owner.
- Invitations can no longer be created for a foreign workspace, and a
  redeemer who is already a member (or a full workspace) is refused.
- Production refuses the default JWT secret; API docs are hidden in
  production; a failed migration aborts startup instead of serving.
- Login and register no longer reveal whether an email exists; inactive
  accounts are rejected; /auth/refresh is rate limited.
- The FK scraper writes debug artefacts only when explicitly enabled,
  logs no scraped values or page text, clears the BankID QR as soon as it
  is scanned and purges finished sessions after five minutes.
- Real FK page captures are removed from the tree (history rewrite
  follows); the parser tests use a synthetic fixture.

Performance and correctness
- Plan apply/sync run inside one locked transaction with batched writes
  instead of one commit per row, so a failure mid-batch leaves nothing
  half-applied and concurrent syncs no longer corrupt each other.
- SQLite runs in WAL mode with a busy timeout; 14 indexes cover the
  filters that were full scans; argon2 hashing runs off the event loop;
  responses are gzipped.
- Frontend: a 401 now refreshes the token once and retries, so sessions
  no longer die silently after 15 minutes; every data hook discards
  stale responses; logout clears state even when the server call fails.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CsXCCcDfmV4Sps4ZQSvNEY

backend/.env.example

@@ -1,14 +1,33 @@
 # Copy to .env and fill in values for local development.
 # Pydantic-settings reads these with the APP_ prefix.
 
+# Deployment environment: development | test | production.
+# In production, Settings refuses to start unless APP_JWT_SECRET is set to a
+# random value of >=32 chars (see app/config.py). Also gates /docs, /redoc,
+# and /openapi.json (disabled in production).
+APP_ENV=development
+
 # Enable FK scraper (legal cleared 2026-06; requires `playwright install chromium`)
 APP_SCRAPER_ENABLED=true
 
+# Scraper debug artifacts (HTML dump + full-page screenshot of the logged-in
+# FK page, saved on error) — OFF by default. CONTAINS PERSONAL DATA (name,
+# balances, payout amounts) when enabled. Only turn on for local debugging on
+# a machine you control, and delete the directory afterwards. Both must be
+# set to actually enable saving.
+# APP_SCRAPER_DEBUG_ENABLED=true
+# APP_SCRAPER_DEBUG_DIR=./debug/scraper
+
 # Database (default: SQLite in repo root)
 # APP_SQLITE_PATH=./foraldraledig.db
 
-# JWT secret — change in production (min 32 chars)
+# JWT secret — REQUIRED in production (min 32 chars). Generate with:
+#   python -c "import secrets; print(secrets.token_urlsafe(48))"
 # APP_JWT_SECRET=dev-secret-change-in-production-min-32-chars
 
 # CORS — add your frontend origin(s)
 # APP_CORS_ORIGINS=["http://localhost:5173"]
+
+# Log level (default: INFO). Avoid DEBUG in production — scraper/auth code
+# paths log more detail at DEBUG.
+# APP_LOG_LEVEL=INFO