sync: encrypted cloud backup for portfolios + settings UX rework

Adds opt-in client-side-encrypted portfolio sync (paid). Browser
PBKDF2(PIN) → AES-GCM, server HKDF(pepper, user_id) outer wrap;
server stores opaque bytes only. Sliding-window rate limit on GET.

  - new portfolio_sync table (migration 0015)
  - POST/GET/DELETE /api/portfolio/sync + /status
  - app/services/portfolio_sync.py crypto + rate limit
  - app/routers/sync.py paid-gated
  - app/static/js/portfolio-sync.js WebCrypto wrapper
  - settings page: enable/disable + PIN modal
  - PORTFOLIO_SYNC_PEPPER setting (warn on startup if missing)

Settings + import rework:

  - /upload merged into /settings#import (legacy route 302s)
  - drop CSV → auto-parse → preview → Import only / Import & sync
  - nav slimmed to Dashboard / News / Log
  - Settings + Logout moved to a user dropdown
  - brand logo links to /

Collateral fixes:

  - settings 500: re-fetch User in current session before mutating
    referral_code (assign_code_if_missing was refreshing a User
    loaded in the auth dep's now-closed session)
  - csv_import: distinct error for unfunded T212 pies (all qty=0)
  - db.py: drop pool_pre_ping (aiomysql 0.3.2 incompat); pin
    isolation_level=READ COMMITTED to avoid gap-lock deadlocks
  - alembic env: disable_existing_loggers=False so in-process
    migrations don't silence uvicorn's loggers
  - docker-compose.override.yml: dev-only volume mount + --reload

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

pyproject.toml

@@ -18,6 +18,7 @@ dependencies = [
     "tenacity>=9.0",
     "structlog>=24.4",
     "argon2-cffi>=23.1",
+    "cryptography>=43.0",
     "itsdangerous>=2.2",
     "email-validator>=2.2",
     "aiosmtplib>=3.0",