Accounting: selectable-source / multi-line manual deposits

Deposits no longer force the credit side through Undeposited Funds — the
structural cause of negative Undeposited balances. A deposit can now credit any
account(s): interest income, a refund, an insurance reimbursement, cash straight
to the bank, etc.

- Schema: add accounting.deposit_lines (deposit_id, company_id, account_id,
  amount, memo) for the credit side, plus deposits.source_account_id as a
  single-source fallback. RLS mirrors deposits (staff + company member).
- post_deposit_gl: Dr bank for the total; Cr each deposit_lines row's account
  for its amount; no lines -> Cr source_account_id; neither -> Cr Undeposited
  Funds (backward compatible — existing deposits stay Dr Bank / Cr Undeposited).
  Remainder safety net keeps the entry balanced. New trg_acct_deposit_line_gl
  re-posts when lines change (header trigger fires before lines exist).
- Make Deposit page: GL-driven submit writes the deposit header + deposit_lines
  and marks selected payments deposited. Adds an "Other deposit lines" grid
  (account + amount + memo) alongside the existing Undeposited selection, with a
  running grand total and a soft guard against over-crediting Undeposited.
  Drops the old bank/Undeposited register-transaction inserts and manual balance
  pokes (never exercised in production; carried a money-in sign bug). Deposits
  are GL-only, consistent with the sync-created deposits already in the DB.

Verified Dr/Cr for single-source and multi-line scenarios against the live GL.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

supabase/migrations/20260604130000_deposit_lines_selectable_source.sql

@@ -0,0 +1,53 @@
+-- Manual Deposits: let a deposit's source (credit) account be selectable instead of
+-- always Undeposited Funds, and support multi-line deposits. This removes the forced
+-- routing through Undeposited Funds (the structural cause of negative Undeposited
+-- balances) and lets a deposit book interest income, refunds, reimbursements, etc.
+
+-- Single-source fallback: a deposit with no lines credits this account (default
+-- Undeposited Funds when null), keeping the existing "deposit received payments" flow.
+alter table accounting.deposits
+  add column if not exists source_account_id uuid references accounting.accounts(id);
+
+-- Multi-line credits: one deposit = Dr Bank (total) and a set of credit lines, each
+-- with its own account and amount. The deposit's amount equals the sum of its lines.
+create table if not exists accounting.deposit_lines (
+  id uuid primary key default gen_random_uuid(),
+  deposit_id uuid not null references accounting.deposits(id) on delete cascade,
+  company_id uuid not null references accounting.companies(id) on delete cascade,
+  account_id uuid not null references accounting.accounts(id),
+  amount numeric not null default 0,
+  memo text,
+  created_at timestamptz not null default now()
+);
+create index if not exists idx_deposit_lines_deposit on accounting.deposit_lines(deposit_id);
+
+alter table accounting.deposit_lines enable row level security;
+
+drop policy if exists "Accounting staff full access" on accounting.deposit_lines;
+create policy "Accounting staff full access" on accounting.deposit_lines
+  for all to authenticated
+  using (accounting.is_accounting_staff()) with check (accounting.is_accounting_staff());
+
+drop policy if exists "Members CRUD deposit_lines" on accounting.deposit_lines;
+create policy "Members CRUD deposit_lines" on accounting.deposit_lines
+  for all to authenticated
+  using (accounting.is_company_member(company_id, auth.uid()))
+  with check (accounting.is_company_member(company_id, auth.uid()));
+
+grant select, insert, update, delete on accounting.deposit_lines to authenticated, service_role;
+
+-- The deposit header trigger posts GL on insert (before any lines exist), so re-post
+-- whenever the lines change too. post_deposit_gl clears + reposts, so this is idempotent.
+create or replace function accounting.tg_deposit_line_gl()
+  returns trigger language plpgsql security definer set search_path to 'public', 'accounting' as $$
+begin
+  begin
+    perform accounting.post_deposit_gl(coalesce(new.deposit_id, old.deposit_id));
+  exception when others then raise warning 'accounting: deposit line GL post failed: %', sqlerrm; end;
+  return coalesce(new, old);
+end$$;
+
+drop trigger if exists trg_acct_deposit_line_gl on accounting.deposit_lines;
+create trigger trg_acct_deposit_line_gl
+  after insert or update or delete on accounting.deposit_lines
+  for each row execute function accounting.tg_deposit_line_gl();