feat: the server checks the grade against the files before approving

The price depends on the grade, which the browser worked out and the API
took on trust. Before a cart is approved at checkout the API now recomputes
it from the uploaded files by the Site's own rules: the pixel size in a
PNG, JPG or WebP header across the printed width (rotation included), and
the area-weighted DPI of the images placed in a PDF of up to 150 MB, 300
for vectors. Sheets take the worst grade, artworks the average. A claim more
than 2 points above the file's grade, or a discount on a file the server
cannot grade, waits for an operator, with the reason on the Kanban.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/schema.sql

@@ -142,6 +142,10 @@ CREATE TABLE IF NOT EXISTS dtf_local.backups (
 );
 CREATE INDEX IF NOT EXISTS backups_finished ON dtf_local.backups(finished_at DESC);
 
+-- Why a quote waits for review, when the reason came from its files (the grade
+-- the server recomputed) and cannot be worked out again from the draft alone.
+ALTER TABLE dtf_local.quotes ADD COLUMN IF NOT EXISTS review_note text;
+
 CREATE INDEX IF NOT EXISTS uploads_owner ON dtf_local.uploads(owner);
 
 -- Indexes follow the queries the application actually issues. Only these; every