* test(taxes): cover compound_tax API semantics and validate it as boolean
* feat(taxes): restore the compound tax toggle in tax type settings
* feat(taxes): compute document-level compound tax amounts
Two-pass recalculation: simple taxes on the discounted subtotal, compound
taxes on the subtotal plus all simple taxes (v2 parity; branch order
fixed -> compound -> inclusive back-out -> simple). Amounts now also
recalculate on tax add/remove and on the tax-inclusive toggle, which
previously never triggered recalculation.
* feat(taxes): support compound taxes in per-item mode
Per-item tax rows now carry the compound flag and charge compound taxes
on the item's discounted base plus its simple taxes, through the same
calcTaxAmount branch order as document-level taxes. The item row splits
its tax sums into simple and compound so a compound row can never widen
its own base.
Also fixes two pre-existing bugs: the per-item tax dropdown read
window.__taxTypes, which nothing ever assigned, so it always rendered
empty (tax types are now fetched by the items table and passed down);
and removing a tax row hard-zeroed the item's totals instead of
re-syncing them.
* fix(invoices): skip placeholder tax rows when persisting item taxes
The document form keeps one empty placeholder tax row per item in
per-item tax mode. Its empty name is nullified by the framework's
empty-string middleware, so inserting it violated the NOT NULL
constraint and turned every per-item save into a 500. The equivalent
v2 guard keyed on a null amount, which the v3 stub (amount: 0) evades;
keying on the missing tax_type_id catches it.
Darko Gjorgjijoski