fix(settings): add SFM Forward tab to settings dialog (v1.5.1)

v1.5.0 shipped the forwarder module + INI keys but the settings
dialog wasn't extended, so the only way operators could enable
forwarding was hand-editing config.ini.  This adds a sixth tab
("SFM Forward") with:

  - Forward events to SFM    checkbox
  - SFM Server URL           entry + Test button (GETs /health)
  - Forward Interval (sec)   spinbox
  - Quiescence (sec)         spinbox
  - Missing-Report Grace     spinbox
  - HTTP Timeout             spinbox
  - State File               entry + Browse...

Save-time guard: enabling the forwarder without a URL raises a
validation error rather than silently saving a non-functional
config.

Patch release — same on-disk INI schema, no config migration.

CHANGELOG.md

@@ -6,6 +6,16 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ---
 
+## [1.5.1] - 2026-05-10
+
+### Added
+- **SFM Forward tab in the Settings dialog.**  v1.5.0 shipped the `event_forwarder.py` module + INI keys but missed the GUI; operators had to edit `config.ini` by hand to enable forwarding.  The settings dialog now exposes:
+  - **Forward events to SFM** checkbox
+  - **SFM Server URL** entry with a **Test** button (mirrors the Connection tab — GETs `/health` and shows the result)
+  - **Forward Interval / Quiescence / Missing-Report Grace / HTTP Timeout** spinboxes
+  - **State File** entry with a Browse... button (defaults to `<log dir>/sfm_forwarded.json` when blank)
+- Save-time guard: enabling SFM Forward without filling in the URL shows a validation error rather than silently saving a non-functional config.
+
 ## [1.5.0] - 2026-05-09
 
 ### Added