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/app/api/router.py

@@ -1,6 +1,6 @@
 from fastapi import APIRouter
 
-from app.api.v1 import auth, users, accounts, categories, transactions, budgets, reports, investments, predictions
+from app.api.v1 import auth, users, accounts, categories, transactions, budgets, reports, investments, predictions, admin
 
 router = APIRouter()
 router.include_router(auth.router, prefix="/auth", tags=["auth"])
@@ -12,3 +12,4 @@ router.include_router(budgets.router)
 router.include_router(reports.router)
 router.include_router(investments.router)
 router.include_router(predictions.router)
+router.include_router(admin.router)