LINUS ROUND 1: Delete dead code (rust/c), generic Store[T], tests, slim main.go

- Removed rust-service/, c-runtime/, kafka stubs
- Generic Store[T] pattern with real tests
- Slimmed main.go from 324 to ~50 lines
- Added config, middleware, store, ledger, pdf tests
- Frontend SPA shell with router
- Binary: 15.5MB -> 12MB

backend/models/models.go

@@ -0,0 +1,106 @@
+// Package models contains domain entities.
+// No SQL, no JSON tags for external APIs — pure domain.
+package models
+
+import (
+	"database/sql"
+	"time"
+
+	"github.com/lib/pq"
+)
+
+// Customer represents a CRM customer
+type Customer struct {
+	ID         string
+	TenantID   string
+	Name       string
+	Email      string
+	Phone      string
+	Company    string
+	OrgNumber  string
+	Status     string
+	Source     string
+	Tags       []string
+	AssignedTo *string
+	CreatedAt  time.Time
+	UpdatedAt  time.Time
+}
+
+// ScanRow scans a sql.Rows into Customer
+func (c *Customer) ScanRow(rows *sql.Rows) error {
+	var tags pq.StringArray
+	err := rows.Scan(&c.ID, &c.Name, &c.Email, &c.Phone, &c.Company, &c.OrgNumber,
+		&c.Status, &c.Source, &tags, &c.AssignedTo, &c.CreatedAt, &c.UpdatedAt)
+	c.Tags = []string(tags)
+	return err
+}
+
+// ScanOneRow scans a sql.Row into Customer
+func (c *Customer) ScanOneRow(row *sql.Row) error {
+	var tags pq.StringArray
+	err := row.Scan(&c.ID, &c.Name, &c.Email, &c.Phone, &c.Company, &c.OrgNumber,
+		&c.Status, &c.Source, &tags, &c.AssignedTo, &c.CreatedAt, &c.UpdatedAt)
+	c.Tags = []string(tags)
+	return err
+}
+
+// Deal represents a sales opportunity
+type Deal struct {
+	ID            string
+	TenantID      string
+	CustomerID    string
+	ContactID     *string
+	Name          string
+	Description   string
+	Value         float64
+	Currency      string
+	Status        string
+	Stage         string
+	Probability   int
+	ExpectedClose *time.Time
+	ActualClose   *time.Time
+	AssignedTo    *string
+	CreatedAt     time.Time
+	UpdatedAt     time.Time
+}
+
+// ScanRow scans a sql.Rows into Deal
+func (d *Deal) ScanRow(rows *sql.Rows) error {
+	return rows.Scan(&d.ID, &d.TenantID, &d.CustomerID, &d.ContactID, &d.Name,
+		&d.Description, &d.Value, &d.Currency, &d.Status, &d.Stage,
+		&d.Probability, &d.ExpectedClose, &d.ActualClose, &d.AssignedTo,
+		&d.CreatedAt, &d.UpdatedAt)
+}
+
+// ScanOneRow scans a sql.Row into Deal
+func (d *Deal) ScanOneRow(row *sql.Row) error {
+	return row.Scan(&d.ID, &d.TenantID, &d.CustomerID, &d.ContactID, &d.Name,
+		&d.Description, &d.Value, &d.Currency, &d.Status, &d.Stage,
+		&d.Probability, &d.ExpectedClose, &d.ActualClose, &d.AssignedTo,
+		&d.CreatedAt, &d.UpdatedAt)
+}
+
+// Invoice represents a financial invoice
+type Invoice struct {
+	ID         string
+	TenantID   string
+	CustomerID string
+	Amount     float64
+	Currency   string
+	Status     string
+	DueDate    *time.Time
+	PaidAt     *time.Time
+	CreatedAt  time.Time
+}
+
+// ScanRow scans a sql.Rows into Invoice
+func (i *Invoice) ScanRow(rows *sql.Rows) error {
+	return rows.Scan(&i.ID, &i.TenantID, &i.CustomerID, &i.Amount, &i.Currency,
+		&i.Status, &i.DueDate, &i.PaidAt, &i.CreatedAt)
+}
+
+// ScanOneRow scans a sql.Row into Invoice
+func (i *Invoice) ScanOneRow(row *sql.Row) error {
+	return row.Scan(&i.ID, &i.TenantID, &i.CustomerID, &i.Amount, &i.Currency,
+		&i.Status, &i.DueDate, &i.PaidAt, &i.CreatedAt)
+}