fix(forward-log): distinguish histograms from missing-report (v1.5.3)

On machines running histogram-mode units (extensions ending in H,
e.g. H907L1R7.PG0H), every forwarded event was logging "no report"
even though histograms never get auto-exported ASCII reports from
Blastware — making the log look like every forward was misconfigured
when in fact things were working correctly.

Three log states now:

  - Waveform + paired TXT
      → "+ <txt> attached"
  - Waveform without TXT (likely BW config issue)
      → "no report ⚠"
  - Histogram (any flavour)
      → "(histogram, no report expected)"

New is_histogram_event() helper classifies by BW filename extension:
4-char ext ending in H = histogram; old-firmware 3-char extensions
default to non-histogram (safe default — we'd rather flag a missing
report than silently suppress the warning on a real waveform event).

Forwarding logic itself is unchanged — this is purely log clarity.

series3_watcher.py

@@ -247,7 +247,7 @@ def scan_latest(
 
 
 # --- API heartbeat / SFM telemetry helpers ---
-VERSION = "1.5.2"
+VERSION = "1.5.3"
 
 
 def _read_log_tail(log_file: str, n: int = 25) -> Optional[list]: