v3.29.2: the strict row rule for the outfile import

The format is positional: an empty value drops its token, so the parser
now requires every data row to have exactly the header's column count.
That catches an empty value anywhere - including a middle one, which
would otherwise shift the following columns (a missing ADM made the KIC
columns read the KIK values: valid hex, wrong preset) - and a KICn/KIDn
pair declared in the header must carry a usable hex value in every row
(a placeholder fails).

A violation makes the whole file invalid: the report's error names the
line, no presets are returned, and an import (mode) answers 400 - it is
never partially imported.  The PWA disables the Import button while the
report carries an error and guards the call.

Unchanged per-row reports: a non-hex PIN/PUK/ADM/PSK value (dropped, the
card kept), an unsupported key size (that keyset skipped), a card whose
remaining keysets are unusable (skipped).  All three real samples satisfy
the rule exactly (11/11, 18/18, 18/18).

Docs: help EN/RU, api.md, the repo AGENTS.  Tests: the short/long row and
the placeholder-keyset file errors, the valid-file round trip, the
endpoint's refusal (nothing stored), the PWA's disabled button.
926 frontend + 945 Python; sw cache simple-v449.

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'simple-v448';
+const CACHE = 'simple-v449';
 const URLS = [
   'index.html',
   'help.html',