[amar-python]

Refs #107. Part M3c of ART Milestone 3, frontend side. This is stacked on #138, which stores the reasons on the server. Merge #138 first; this PR's base then moves to main.

What it does

• When a migrated file has failed rows, its Preview dialog in Migrated files now loads the stored reasons from GET /api/csv/uploads/{id}. It lists the row, column, value and reason, with an Error report download (CSV).
• The reasons come from the server, so any user in the tenant sees them, not only the browser that uploaded the file. That was the gap on Upload with every row rejected is shown as migrated (171 of 171 rows failed, no warning) #123.

Verification

Check	Result
vitest	14 files, 143 tests passed, 2 of them new (stored-row-errors.test.tsx)
tsc --noEmit	0 errors
eslint on the new test and csv.functions.ts	0 problems
Production build (node-server)	Built
End to end	API (PostgreSQL 16, this stack) and the production frontend, run as a throwaway tenant admin. A CSV with 1 of 3 rows failing was uploaded through the API. A fresh browser context, with no local import history, signed in, opened Preview, and showed "x" is not a whole number for row 2, column n, plus the Error report button. There were 0 page errors

I broke the component to check that the test catches it: with the reason column rendering the column name instead, the test failed (1 failed, 1 passed).

Not in this PR: needs the product owner's call

The #107 scope note also says "include them in audit reports". The audit report today is the Import history page. That page is built entirely from the uploading browser's local storage, so another user's uploads aren't there to report on. There are two ways to close this:

• (a) Move Import history and its exports onto the server's GET /api/csv/uploads now, as an extra M3 part.
• (b) Leave it to M7's "filtered audit reports" (BR-35), which rebuilds reporting on server data anyway.

My recommendation is (b): M7 replaces that page's data source, so doing it in M3 would be done twice.

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