feat(payments): report income to «Мой налог»

The direct rail runs on НПД, where the provider neither files with the tax
service nor issues a receipt — so nobody was doing it. This registers each
rouble purchase, annuls its receipt on a refund, and hands the buyer the
receipt by email.

Two properties of the (unofficial) lknpd API shape the design. Registering an
income takes no idempotency key, so an error does not mean nothing happened:
the service name is frozen before the call and carries a marker from the tail
of the order id, and after a failure the taxpayer's income list is searched
for that exact name. Found means filed; not found halts the queue for a human,
because declaring an income twice is as wrong as not declaring it. And faults
are classified rather than logged: a token is renewed silently, a throttle
backs off, an outage retries, but three unfixable rejections take the rail out
of service — a changed format must not become thousands of requests overnight.

The console button and the worker share one RunBatch. Automatic mode is armed
from the console, not from configuration, so the operator can watch a run go
through by hand first. A daily watchdog runs whether or not it is armed, since
the case it exists for is the export being off. An idle queue issues no call at
all — not even an authentication.

No payment path changed: the purchase letter rides the existing payment-event
outbox on its own cursor, the receipt and annulment letters ride the export
row. Decisions D53-D60.

deploy/docker-compose.yml

@@ -182,6 +182,14 @@ services:
       # Setting a VAT rate code (tag 1199: 1 = «Без НДС», 4 = 20%, 11 = 22%) turns receipts back on
       # — the switch a lost НПД regime would need — with no code change.
       BACKEND_YOOKASSA_VAT_CODE: ${YOOKASSA_VAT_CODE:-}
+      # «Мой налог» (НПД) export. The key is ours, not the tax service's: it seals the cabinet's
+      # refresh token at rest, so the credential survives neither a database dump nor a backup in
+      # readable form. Empty leaves the whole rail dormant — no console section, no workers. The
+      # operator signs in from the console; the password is never stored. The time zone decides
+      # which tax month a near-midnight payment is filed under, so it follows the taxpayer's
+      # registration rather than the server clock.
+      BACKEND_MYNALOG_KEY: ${MYNALOG_KEY:-}
+      BACKEND_MYNALOG_TZ: ${MYNALOG_TZ:-}
     # The dictionary lives on a named volume seeded from the image on first boot
     # (the image's /opt/dawg is owned by the nonroot UID, which the fresh volume
     # inherits). The admin console writes new version subdirectories here, and the