feat(phase-1): TapTrack Hub initial scaffold

Full project scaffold for TapTrack Hub — cloud SaaS control plane
for managing on-prem TapTrack school deployments.

## Infrastructure
- Docker Compose: backend (gunicorn+uvicorn), Celery worker + beat,
  frontend (Vite build + nginx), PostgreSQL 15, Redis 7, nginx proxy
- Dockerfile for backend and frontend, nginx reverse proxy config

## Backend (FastAPI + SQLAlchemy async + Celery)
Database schema (10 tables):
  hub_users, schools, licenses, sms_jobs, sms_credit_ledger,
  invoices, invoice_line_items, school_subscriptions,
  support_tickets, ticket_replies, audit_logs, announcements

Auth: JWT (python-jose) + bcrypt + role-based FastAPI dependencies
  (get_current_user, require_super_admin, require_school_admin)

Routers (11): auth, schools, licenses, sms, billing, tickets,
  users, dashboard, school_portal, announcements, sync

Celery tasks (6):
  sms.process_queue, billing.generate_monthly_invoices,
  billing.send_invoice_email, billing.check_overdue,
  license.check_expiry, reports.send_monthly_reports

Services: SMTP email helper (smtplib + Jinja2)
Seed script: creates super admin admin@taptrack.io

## Frontend (Vue 3 + Vite + Pinia + Tailwind CSS)
Router: 14 routes across super admin + school portal layouts
Stores: Pinia auth store with localStorage persistence
API client: full axios client for all backend endpoints
Layouts: AppLayout (super admin), PortalLayout (school), AuthLayout
Components: AppSidebar, PortalSidebar, SidebarItem, KpiCard,
  StatusBadge, ToastStack
Pages: Login, Dashboard, Schools, SchoolDetail, Licenses, SMS,
  Billing, Tickets, TicketDetail, Users, Announcements, 404
Portal pages: Overview, Billing, SMS Reports, Tickets, Profile

## PAUL Planning Files
- .paul/ROADMAP.md: full 15-phase roadmap with detailed scope
- .paul/STATE.md: current position, tech stack, architecture notes
- .paul/phases/01-setup/01-PLAN.md: complete Phase 1 plan (done)
- .paul/phases/02 through 15: README stubs for all future phases

backend/app/models/billing.py

@@ -0,0 +1,68 @@
+import uuid
+import enum
+from datetime import datetime, timezone, date
+from sqlalchemy import String, Boolean, DateTime, Date, Enum as SAEnum, ForeignKey, Text, Numeric, Integer
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+from app.database import Base
+
+class InvoiceStatus(str, enum.Enum):
+    draft = "draft"
+    sent = "sent"
+    paid = "paid"
+    overdue = "overdue"
+    cancelled = "cancelled"
+
+class BillingCycle(str, enum.Enum):
+    monthly = "monthly"
+    annual = "annual"
+
+class Invoice(Base):
+    __tablename__ = "invoices"
+
+    id: Mapped[str] = mapped_column(String(36), primary_key=True, default=lambda: str(uuid.uuid4()))
+    school_id: Mapped[str] = mapped_column(String(36), ForeignKey("schools.id", ondelete="CASCADE"), nullable=False, index=True)
+    invoice_number: Mapped[str] = mapped_column(String(30), unique=True, nullable=False)
+    status: Mapped[InvoiceStatus] = mapped_column(SAEnum(InvoiceStatus), default=InvoiceStatus.draft, nullable=False)
+    billing_period_start: Mapped[date] = mapped_column(Date, nullable=False)
+    billing_period_end: Mapped[date] = mapped_column(Date, nullable=False)
+    subscription_amount: Mapped[float] = mapped_column(Numeric(12, 2), default=0.0, nullable=False)
+    sms_credit_amount: Mapped[float] = mapped_column(Numeric(12, 2), default=0.0, nullable=False)
+    other_amount: Mapped[float] = mapped_column(Numeric(12, 2), default=0.0, nullable=False)
+    total_amount: Mapped[float] = mapped_column(Numeric(12, 2), nullable=False)
+    currency: Mapped[str] = mapped_column(String(3), default="PHP", nullable=False)
+    due_date: Mapped[date | None] = mapped_column(Date, nullable=True)
+    paid_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
+    payment_method: Mapped[str | None] = mapped_column(String(50), nullable=True)
+    payment_reference: Mapped[str | None] = mapped_column(String(100), nullable=True)
+    notes: Mapped[str | None] = mapped_column(Text, nullable=True)
+    pdf_path: Mapped[str | None] = mapped_column(String(255), nullable=True)
+    email_sent_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=lambda: datetime.now(timezone.utc))
+
+    school: Mapped["School"] = relationship("School", back_populates="invoices")
+    line_items: Mapped[list["InvoiceLineItem"]] = relationship("InvoiceLineItem", back_populates="invoice", cascade="all, delete-orphan")
+
+class InvoiceLineItem(Base):
+    __tablename__ = "invoice_line_items"
+
+    id: Mapped[str] = mapped_column(String(36), primary_key=True, default=lambda: str(uuid.uuid4()))
+    invoice_id: Mapped[str] = mapped_column(String(36), ForeignKey("invoices.id", ondelete="CASCADE"), nullable=False)
+    description: Mapped[str] = mapped_column(String(255), nullable=False)
+    quantity: Mapped[float] = mapped_column(Numeric(10, 2), default=1.0, nullable=False)
+    unit_price: Mapped[float] = mapped_column(Numeric(12, 2), nullable=False)
+    amount: Mapped[float] = mapped_column(Numeric(12, 2), nullable=False)
+
+    invoice: Mapped[Invoice] = relationship("Invoice", back_populates="line_items")
+
+class SchoolSubscription(Base):
+    """Stores billing plan per school."""
+    __tablename__ = "school_subscriptions"
+
+    id: Mapped[str] = mapped_column(String(36), primary_key=True, default=lambda: str(uuid.uuid4()))
+    school_id: Mapped[str] = mapped_column(String(36), ForeignKey("schools.id", ondelete="CASCADE"), unique=True, nullable=False)
+    cycle: Mapped[BillingCycle] = mapped_column(SAEnum(BillingCycle), default=BillingCycle.monthly, nullable=False)
+    monthly_fee: Mapped[float] = mapped_column(Numeric(12, 2), default=0.0, nullable=False)
+    sms_cost_per_message: Mapped[float] = mapped_column(Numeric(8, 4), default=1.0, nullable=False)
+    next_billing_date: Mapped[date | None] = mapped_column(Date, nullable=True)
+    is_active: Mapped[bool] = mapped_column(Boolean, default=True, nullable=False)
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), default=lambda: datetime.now(timezone.utc))