Support decimal rupee prices (paise after the point)

PB number fields are float64 with onlyInt unset, so storage already
accepted decimals — verified 449.5 round-trips via API with no migration.
Cards now format fractional prices as ₹449.50 (whole rupees stay ₹449);
docs and type comments updated.

README.md

@@ -174,7 +174,8 @@ new) and touches nothing else.
 - `name` / `variant` — variants are **separate products** whenever their price differs
   ("Penne Arrabiata" + variant "Veg" ₹589 / "Chicken" ₹639); the POS can group by `name`
 - `description`
-- `price` — number, whole rupees (449 = ₹449)
+- `price` — number, rupees with optional paise after the decimal point
+  (449 = ₹449, 449.5 = ₹449.50)
 - `diet` — select: `veg` / `nonveg` / `mixed` (a bool can't be null in PocketBase, so mixed
   items like Caesar Salad use `mixed`; the site renders no badge for it)
 - `pairing` — optional beer pairing