fix(forward): pair BW ACH ASCII reports using the _ASCII.TXT convention (v1.5.4)

Blastware's official Auto Call Home server writes per-event ASCII
reports as <stem>_<ext>_ASCII.TXT (e.g. N844L20G_630H_ASCII.TXT),
not <binary>.TXT (e.g. N844L20G.630H.TXT).  Versions v1.5.0–v1.5.3
only looked for the latter and silently shipped every binary alone,
so the SFM database lost the per-event Peak Acceleration / Peak
Displacement / ZC Freq / Time of Peak / Peak Vector Sum + time /
sensor self-check fields on every forwarded event.

Fix: pair-finding logic now tries the ACH-convention filename first
and falls back to <binary>.TXT for compatibility with operator-saved
manual exports and existing test fixtures.

  ach_report_name("M529LK44.AB0")    → "M529LK44_AB0_ASCII.TXT"
  legacy_report_name("M529LK44.AB0") → "M529LK44.AB0.TXT"

When both files exist (operator manually saved + ACH auto-exported),
ACH wins because that's the canonical name on modern BW deployments.
Both candidates checked case-insensitively against the cached
directory listing — no extra stat() calls.

6 new unit tests cover the new pairing logic, helper-function
correctness, and the precedence rule.  Total now 31 tests, all green.

Field-deploy note: re-running v1.5.4 on a folder where v1.5.0–v1.5.3
already ran will NOT re-forward historical events — the
sfm_forwarded.json state file remembers them by sha256.  To re-forward
historical events to populate SFM with the now-correctly-paired
reports, delete the state file before starting v1.5.4.

README.md

@@ -1,4 +1,4 @@
-# Series 3 Watcher v1.5.3
+# Series 3 Watcher v1.5.4
 
 Monitors Instantel **Series 3 (Minimate)** call-in activity on a Blastware server. Runs as a **system tray app** that starts automatically on login, reports heartbeats to terra-view, and self-updates from Gitea.
 
@@ -88,7 +88,7 @@ All settings live in `config.ini`. The Setup Wizard covers every field, but here
 | `UPDATE_SOURCE` | `gitea` (default) or `url` — where to check for updates |
 | `UPDATE_URL` | Base URL of the update server when `UPDATE_SOURCE = url` (e.g. terra-view URL). The watcher fetches `/api/updates/series3-watcher/version.txt` and `/api/updates/series3-watcher/series3-watcher.exe` from this base. |
 
-### SFM Event Forwarder (v1.5.3+)
+### SFM Event Forwarder (v1.5.4+)
 
 Forwards each Blastware event binary (and its paired `<binary>.TXT` ASCII report when present) to an SFM server's `/db/import/blastware_file` endpoint, where the report is parsed and the rich per-channel stats (PPV, ZC Freq, Time of Peak, Peak Acceleration / Displacement, sensor self-check) land in a searchable database. **Default-off** — existing deployments keep their old behaviour after auto-updating until the operator opts in.
 
@@ -155,7 +155,7 @@ To view connected watchers: **Settings → Developer → Watcher Manager**.
 
 ## Versioning
 
-Follows **Semantic Versioning**. Current release: **v1.5.3**.
+Follows **Semantic Versioning**. Current release: **v1.5.4**.
 See `CHANGELOG.md` for full history.
 
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