Add municipal receipt module and convert navbar to sidebar

- New module: Municipalidad de Belén receipt extraction via pdftotext+regex
  - Backend: MunicipalReceipt + WaterMeterReading models, upload/list/detail/water-consumption endpoints
  - Auto-creates budget Transaction on upload (duplicate-safe via reference)
  - Frontend: ServiciosMunicipales page with summary cards, water consumption bar chart, receipt history, PDF upload
- Convert top navbar to left sidebar with section headers (General, Finanzas, Servicios)
  - Desktop: fixed 220px sidebar, mobile: sheet overlay
  - Grouped nav: Dashboard | Presupuesto, Salarios, Pensiones, Analytics | Municipalidad

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/models/models.py

@@ -358,3 +358,75 @@ class BalanceOverrideRead(SQLModel):
     month: int
     override_balance: float
     updated_at: datetime
+
+
+# --- Municipal Receipt ---
+
+
+class MunicipalReceiptBase(SQLModel):
+    receipt_date: date
+    due_date: date
+    period: str  # "YYYY-MM"
+    account: str
+    finca: str
+    holder_name: str
+    holder_cedula: str
+    holder_address: str
+    subtotal: float
+    interests: float
+    iva: float
+    total: float
+    raw_charges: list[dict] = Field(
+        default_factory=list,
+        sa_column=Column(JSON, nullable=False, server_default="[]"),
+    )
+    source_filename: str
+
+
+class MunicipalReceipt(MunicipalReceiptBase, table=True):
+    __table_args__ = (UniqueConstraint("account", "period"),)
+    id: Optional[int] = Field(default=None, primary_key=True)
+    created_at: datetime = Field(default_factory=datetime.utcnow)
+    water_readings: list["WaterMeterReading"] = Relationship(
+        back_populates="receipt",
+    )
+
+
+class MunicipalReceiptCreate(MunicipalReceiptBase):
+    pass
+
+
+class MunicipalReceiptRead(MunicipalReceiptBase):
+    id: int
+    created_at: datetime
+
+
+# --- Water Meter Reading ---
+
+
+class WaterMeterReadingBase(SQLModel):
+    meter_id: str
+    period: str  # "YYYY-MM"
+    reading_previous: float = 0
+    reading_current: float = 0
+    consumption_m3: float
+    agua_potable: float = 0
+    serv_ambientales: float = 0
+    alcant_sanitario: float = 0
+    iva: float = 0
+    is_historical: bool = False
+    receipt_id: Optional[int] = Field(default=None, foreign_key="municipalreceipt.id")
+
+
+class WaterMeterReading(WaterMeterReadingBase, table=True):
+    __table_args__ = (UniqueConstraint("meter_id", "period", "is_historical"),)
+    id: Optional[int] = Field(default=None, primary_key=True)
+    created_at: datetime = Field(default_factory=datetime.utcnow)
+    receipt: Optional[MunicipalReceipt] = Relationship(
+        back_populates="water_readings",
+    )
+
+
+class WaterMeterReadingRead(WaterMeterReadingBase):
+    id: int
+    created_at: datetime