Charge tuition automatically from attendance

Adds a per-student daily rate (students.daily_tuition_cents) and a trigger
that writes a tuition charge when a student is marked present or late.

Idempotency is the crux. The attendance UI upserts on (student_id, date)
and teachers toggle a status freely — present, absent, present again. A
naive "insert a charge on attendance" trigger bills the family once per
click. So each auto-charge is bound to the attendance row that caused it
via ledger_entries.attendance_id (UNIQUE), which turns the write into an
upsert, lets a change back to absent delete the charge, and cascades the
charge away if the attendance record is deleted.

Manual entries keep attendance_id NULL — Postgres allows unlimited NULLs
in a unique index — so hand-entered charges are untouched and the UI can
tell auto from manual.

A NULL rate (the default) means never auto-charge, so nothing begins
billing until a rate is deliberately set on a student. Existing
attendance is not backfilled: retroactively generating charges against
families' balances should be an explicit decision, not a side effect of
deploying a migration.

The trigger is SECURITY DEFINER because the writer is a teacher marking
attendance while ledger_entries is admin-write under RLS; teachers gain
no general ledger access, only this fixed attendance-derived write.

Verified against the live schema across all eight paths: charge on
present, reversal on absent, no duplicate on re-mark, late billable,
excused free, no rate means no charge, rate change on re-save, and
cascade on attendance delete.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/integrations/supabase/types.ts

@@ -480,6 +480,7 @@ export type Database = {
       ledger_entries: {
         Row: {
           amount_cents: number
+          attendance_id: string | null
           category: Database["public"]["Enums"]["ledger_category"]
           created_at: string
           created_by: string | null
@@ -491,6 +492,7 @@ export type Database = {
         }
         Insert: {
           amount_cents: number
+          attendance_id?: string | null
           category?: Database["public"]["Enums"]["ledger_category"]
           created_at?: string
           created_by?: string | null
@@ -502,6 +504,7 @@ export type Database = {
         }
         Update: {
           amount_cents?: number
+          attendance_id?: string | null
           category?: Database["public"]["Enums"]["ledger_category"]
           created_at?: string
           created_by?: string | null
@@ -512,6 +515,13 @@ export type Database = {
           student_id?: string
         }
         Relationships: [
+          {
+            foreignKeyName: "ledger_entries_attendance_id_fkey"
+            columns: ["attendance_id"]
+            isOneToOne: true
+            referencedRelation: "attendance"
+            referencedColumns: ["id"]
+          },
           {
             foreignKeyName: "ledger_entries_student_id_fkey"
             columns: ["student_id"]
@@ -1159,6 +1169,7 @@ export type Database = {
           class_id: string | null
           created_at: string
           custody_agreement: string | null
+          daily_tuition_cents: number | null
           disciplinary_history: string | null
           dismissal_methods: string[]
           dismissal_other: string | null
@@ -1192,6 +1203,7 @@ export type Database = {
           class_id?: string | null
           created_at?: string
           custody_agreement?: string | null
+          daily_tuition_cents?: number | null
           disciplinary_history?: string | null
           dismissal_methods?: string[]
           dismissal_other?: string | null
@@ -1225,6 +1237,7 @@ export type Database = {
           class_id?: string | null
           created_at?: string
           custody_agreement?: string | null
+          daily_tuition_cents?: number | null
           disciplinary_history?: string | null
           dismissal_methods?: string[]
           dismissal_other?: string | null