chore(release): consolidate v1.5.1–v1.5.4 into single v1.5.0 Unreleased entry

None of v1.5.1 / v1.5.2 / v1.5.3 / v1.5.4 ever shipped — they only
existed as separate CHANGELOG entries on this unmerged feature
branch.  SemVer ties version numbers to releases, not commits.
From a field machine's perspective, the world skips straight from
v1.4.4 to whatever the next built-and-pushed installer is tagged.

Revert VERSION / AppVersion / module-docstring version comments
to v1.5.0 across:
  - series3_watcher.py     (VERSION = "1.5.0")
  - installer.iss          (AppVersion=1.5.0)
  - series3_tray.py        (docstring)
  - settings_dialog.py     (docstring)
  - README.md              (banner + footer)

Consolidate the four split CHANGELOG sections into a single
"## [Unreleased] — v1.5.0" entry covering all the work in one
release.  Configuration key table consolidated into one place.
No commit history rewriting — the per-commit code changes still
make sense as logical units for code review; only the surface-
level version metadata + CHANGELOG narrative was misleading.

Going forward: accumulate work-in-progress under an "[Unreleased]"
heading, bump VERSION only at actual release time.

README.md

@@ -1,4 +1,4 @@
-# Series 3 Watcher v1.5.4
+# Series 3 Watcher v1.5.0
 
 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 (v1.5.4+)
+### SFM Event Forwarder (v1.5.0+)
 
 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: **v1.5.4**.
+Follows **Semantic Versioning**. Current release: **v1.5.0**.
 See `CHANGELOG.md` for full history.
 
 ---