Stop one lost extrinsic from silencing the noter bot (#30)

Every report waits behind the previous one, and a submission only settled
when it reached a block. One the pool dropped, rejected or replaced never
settled, so every report queued after it waited forever. The watchdog meant
to catch a silent bot was armed only after the first scan returned, so when
that first scan was the one that hung there was no watchdog at all: the
production container logged its last line one minute after starting on
2026-10-13 and stayed up, silent, for more than a day.

- submit.js: a submission settles on a terminal status (Dropped, Invalid,
  Usurped, FinalityTimeout) or after SUBMIT_TIMEOUT_MS, and releases its
  status subscription.
- The watchdog is armed before connecting and counts from the process start
  until a scan completes, so a heartbeat left by an earlier process in the
  same container does not count for this one.
- The noter's own account is skipped: the chain refuses a noter's report
  about themselves, so it failed in every scan.
- Unit tests for both rules, run inside the noter image in CI.

noter/Dockerfile

@@ -10,6 +10,6 @@ WORKDIR /app
 COPY package.json package-lock.json ./
 RUN npm ci --omit=dev --omit=optional --no-audit --no-fund
 
-COPY bot.js ./
+COPY bot.js submit.js ./
 
 CMD ["node", "bot.js"]