Complete Phase 3, Phase 5 polish and hardening

Phase 3 — Investments:
- Multi-currency support: holdings track purchase currency, FX rates convert to base for totals
- Capital gains report using UK Section 104 pool method, grouped by tax year
- Capital Gains tab added to Reports page

Phase 5 — Polish & Hardening:
- Mobile-responsive layout: bottom nav, sidebar hidden on mobile, logo in TopBar, compact header buttons, hover-only actions now always visible on touch
- Backup system: encrypted GPG backups via backup.sh, nightly scheduler job, admin API (list/trigger/download/restore), Settings UI with drag-to-restore confirmation
- Docker entrypoint with gosu privilege drop to fix bind-mount ownership on fresh deployments
- OWASP fixes: refresh token now bound to its session (new refresh_token_hash column + migration), CSRF secure flag tied to environment, IP-level rate limiting on login, TOTPEnableRequest Pydantic schema replaces raw dict
- AES-256-GCM key rotation script (rotate_keys.py) with dry-run mode and atomic DB transaction
- CLAUDE.md added for AI-assisted development context
- README updated: correct reverse proxy port, accurate backup/restore commands, key rotation instructions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/scripts/rotate_keys.sh

@@ -0,0 +1,54 @@
+#!/bin/bash
+# rotate_keys.sh — re-encrypt all AES-256-GCM fields with a new key.
+# The application must be STOPPED before running.
+#
+# Usage:
+#   NEW_ENCRYPTION_KEY=$(python3 -c "import secrets; print(secrets.token_hex(32))")
+#   docker compose stop backend
+#   NEW_ENCRYPTION_KEY="$NEW_ENCRYPTION_KEY" ./scripts/rotate_keys.sh
+#   # On success, update ENCRYPTION_KEY in .env, then:
+#   docker compose up -d backend
+set -euo pipefail
+
+if [ -z "${NEW_ENCRYPTION_KEY:-}" ]; then
+  echo "ERROR: NEW_ENCRYPTION_KEY is not set"
+  echo "Generate with: python3 -c \"import secrets; print(secrets.token_hex(32))\""
+  exit 1
+fi
+
+if [ -z "${ENCRYPTION_KEY:-}" ]; then
+  # Try to load from .env in the project root
+  ENV_FILE="$(dirname "$0")/../.env"
+  if [ -f "${ENV_FILE}" ]; then
+    ENCRYPTION_KEY=$(grep -E '^ENCRYPTION_KEY=' "${ENV_FILE}" | cut -d= -f2- | tr -d '"' | tr -d "'")
+  fi
+fi
+
+if [ -z "${ENCRYPTION_KEY:-}" ]; then
+  echo "ERROR: ENCRYPTION_KEY (current key) could not be found in environment or .env"
+  exit 1
+fi
+
+if [ "${ENCRYPTION_KEY}" = "${NEW_ENCRYPTION_KEY}" ]; then
+  echo "ERROR: NEW_ENCRYPTION_KEY is the same as the current key — nothing to do"
+  exit 1
+fi
+
+echo "[rotate] This will re-encrypt ALL sensitive fields in the database."
+echo "[rotate] Ensure the application containers are stopped before continuing."
+read -r -p "[rotate] Type 'yes' to continue: " CONFIRM
+if [ "${CONFIRM}" != "yes" ]; then
+  echo "[rotate] Aborted"
+  exit 1
+fi
+
+echo "[rotate] Running key rotation inside the backend container…"
+docker compose exec \
+  -e ENCRYPTION_KEY="${ENCRYPTION_KEY}" \
+  -e NEW_ENCRYPTION_KEY="${NEW_ENCRYPTION_KEY}" \
+  backend python -m app.core.key_rotation
+
+echo ""
+echo "[rotate] SUCCESS. Next steps:"
+echo "  1. Update ENCRYPTION_KEY in .env to: ${NEW_ENCRYPTION_KEY}"
+echo "  2. Restart the backend: docker compose up -d backend"