fix: batch A - crash bugs, a leak, and startup/edge fragility

Seven confirmed defects from the code audit, each small and low-risk.

* ai_functions.get_random_cyclic_message: random.randint(0, len(CYCLIC_WORDS))
  is inclusive -> could return len -> IndexError. Now randrange(len) + guard on
  an empty CYCLIC_WORDS.
* librarian_commands.get_image_sadox: random.randrange(0, len(res)-1) never
  picked the last comic and raised ValueError('empty range') on a single file.
  Now randrange(len) + an empty-dir guard.
* ai_commands image generation: every DALL-E error branch replied but did not
  return, so control fell through to `if response:` with response unbound ->
  UnboundLocalError right after the friendly message. Each branch now returns;
  response is pre-initialised; and PermissionDeniedError no longer passes a
  (message, text) tuple as a single arg.
* search_bot DOI match: `item["DOI"] in data` was a substring test, so a DOI
  that is a prefix of a longer one (10.1/1 vs 10.1/12) produced a false 'exists'
  hit. Now matches the line's first whitespace token exactly, via an O(1) dict
  index built once per consumer (also removes the O(queried-DOIs) per-line scan
  - a real win for large databases).
* communication_subroutine.scan_incoming: matched records were never removed
  from awaiting_q, so it grew unbounded over uptime and a reused UUID could
  re-match a stale record. Matched records are now dropped after dispatch.
* communication_subroutine.id3: (resp.headers.get("icy-name") or "").title()
  guards against a stream that omits headers (was AttributeError on None,
  500-ing the /prepped_tracks "next" handler).
* betoniarka.scan_tracks: waits for the radio logs to exist instead of dying
  with FileNotFoundError on a fresh deploy (which silently killed the
  now-playing forwarder until a restart).

Verified: tests/unit/test_search_bot.py gains exact-match and trailing-metadata
cases; full unit job 43 passed. Remaining observations (image-gen stale
/home/pi fallback paths + dead FileNotFoundError-after-OSError branch; tailer
still vulnerable to mid-run log rotation; DOI-first-token assumption) noted for
follow-up - none are crashes on the normal path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

conjurer_betoniarka/betoniarka.py

@@ -203,6 +203,12 @@ def wyszukaj(word_list, how_many, _logger=None, write_to=None):
 # ---------------------------------------------------------------- tailer
 def scan_tracks():
     """Tail the radio logs and forward play events to the bot."""
+    # On a fresh deploy Liquidsoap may not have written its logs yet; wait for
+    # them instead of dying with FileNotFoundError, which used to silently kill
+    # the now-playing forwarder until the container was restarted.
+    while not (RADIOLOG_PATH.exists() and PERSISTENCE_PATH.exists()):
+        logger.info("Waiting for radio logs (%s, %s)...", RADIOLOG_PATH, PERSISTENCE_PATH)
+        time.sleep(5)
     with open(RADIOLOG_PATH, "r", encoding=ENCODING) as log_file:
         log_file.seek(os.stat(RADIOLOG_PATH).st_size)
         prev_size = os.stat(PERSISTENCE_PATH).st_size