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>

docker-compose.override.yml

@@ -5,5 +5,13 @@
 
 services:
   app:
+    # Dev: mount the source over the image's copy so edits on the host
+    # land in the container without a rebuild; `--reload` restarts uvicorn
+    # when a file changes. Prod bakes the code into the image (Dockerfile)
+    # and uses the plain command from docker-compose.yml.
+    command: ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000",
+              "--workers", "1", "--reload", "--reload-dir", "/app/app"]
+    volumes:
+      - ./app:/app/app
     ports:
       - "${CASSANDRA_PORT:-8000}:8000"